v4.19.13 snapshot.
diff --git a/Documentation/driver-api/dmaengine/client.rst b/Documentation/driver-api/dmaengine/client.rst
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+====================
+DMA Engine API Guide
+====================
+
+Vinod Koul <vinod dot koul at intel.com>
+
+.. note:: For DMA Engine usage in async_tx please see:
+ ``Documentation/crypto/async-tx-api.txt``
+
+
+Below is a guide to device driver writers on how to use the Slave-DMA API of the
+DMA Engine. This is applicable only for slave DMA usage only.
+
+DMA usage
+=========
+
+The slave DMA usage consists of following steps:
+
+- Allocate a DMA slave channel
+
+- Set slave and controller specific parameters
+
+- Get a descriptor for transaction
+
+- Submit the transaction
+
+- Issue pending requests and wait for callback notification
+
+The details of these operations are:
+
+1. Allocate a DMA slave channel
+
+ Channel allocation is slightly different in the slave DMA context,
+ client drivers typically need a channel from a particular DMA
+ controller only and even in some cases a specific channel is desired.
+ To request a channel dma_request_chan() API is used.
+
+ Interface:
+
+ .. code-block:: c
+
+ struct dma_chan *dma_request_chan(struct device *dev, const char *name);
+
+ Which will find and return the ``name`` DMA channel associated with the 'dev'
+ device. The association is done via DT, ACPI or board file based
+ dma_slave_map matching table.
+
+ A channel allocated via this interface is exclusive to the caller,
+ until dma_release_channel() is called.
+
+2. Set slave and controller specific parameters
+
+ Next step is always to pass some specific information to the DMA
+ driver. Most of the generic information which a slave DMA can use
+ is in struct dma_slave_config. This allows the clients to specify
+ DMA direction, DMA addresses, bus widths, DMA burst lengths etc
+ for the peripheral.
+
+ If some DMA controllers have more parameters to be sent then they
+ should try to embed struct dma_slave_config in their controller
+ specific structure. That gives flexibility to client to pass more
+ parameters, if required.
+
+ Interface:
+
+ .. code-block:: c
+
+ int dmaengine_slave_config(struct dma_chan *chan,
+ struct dma_slave_config *config)
+
+ Please see the dma_slave_config structure definition in dmaengine.h
+ for a detailed explanation of the struct members. Please note
+ that the 'direction' member will be going away as it duplicates the
+ direction given in the prepare call.
+
+3. Get a descriptor for transaction
+
+ For slave usage the various modes of slave transfers supported by the
+ DMA-engine are:
+
+ - slave_sg: DMA a list of scatter gather buffers from/to a peripheral
+
+ - dma_cyclic: Perform a cyclic DMA operation from/to a peripheral till the
+ operation is explicitly stopped.
+
+ - interleaved_dma: This is common to Slave as well as M2M clients. For slave
+ address of devices' fifo could be already known to the driver.
+ Various types of operations could be expressed by setting
+ appropriate values to the 'dma_interleaved_template' members.
+
+ A non-NULL return of this transfer API represents a "descriptor" for
+ the given transaction.
+
+ Interface:
+
+ .. code-block:: c
+
+ struct dma_async_tx_descriptor *dmaengine_prep_slave_sg(
+ struct dma_chan *chan, struct scatterlist *sgl,
+ unsigned int sg_len, enum dma_data_direction direction,
+ unsigned long flags);
+
+ struct dma_async_tx_descriptor *dmaengine_prep_dma_cyclic(
+ struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len,
+ size_t period_len, enum dma_data_direction direction);
+
+ struct dma_async_tx_descriptor *dmaengine_prep_interleaved_dma(
+ struct dma_chan *chan, struct dma_interleaved_template *xt,
+ unsigned long flags);
+
+ The peripheral driver is expected to have mapped the scatterlist for
+ the DMA operation prior to calling dmaengine_prep_slave_sg(), and must
+ keep the scatterlist mapped until the DMA operation has completed.
+ The scatterlist must be mapped using the DMA struct device.
+ If a mapping needs to be synchronized later, dma_sync_*_for_*() must be
+ called using the DMA struct device, too.
+ So, normal setup should look like this:
+
+ .. code-block:: c
+
+ nr_sg = dma_map_sg(chan->device->dev, sgl, sg_len);
+ if (nr_sg == 0)
+ /* error */
+
+ desc = dmaengine_prep_slave_sg(chan, sgl, nr_sg, direction, flags);
+
+ Once a descriptor has been obtained, the callback information can be
+ added and the descriptor must then be submitted. Some DMA engine
+ drivers may hold a spinlock between a successful preparation and
+ submission so it is important that these two operations are closely
+ paired.
+
+ .. note::
+
+ Although the async_tx API specifies that completion callback
+ routines cannot submit any new operations, this is not the
+ case for slave/cyclic DMA.
+
+ For slave DMA, the subsequent transaction may not be available
+ for submission prior to callback function being invoked, so
+ slave DMA callbacks are permitted to prepare and submit a new
+ transaction.
+
+ For cyclic DMA, a callback function may wish to terminate the
+ DMA via dmaengine_terminate_async().
+
+ Therefore, it is important that DMA engine drivers drop any
+ locks before calling the callback function which may cause a
+ deadlock.
+
+ Note that callbacks will always be invoked from the DMA
+ engines tasklet, never from interrupt context.
+
+4. Submit the transaction
+
+ Once the descriptor has been prepared and the callback information
+ added, it must be placed on the DMA engine drivers pending queue.
+
+ Interface:
+
+ .. code-block:: c
+
+ dma_cookie_t dmaengine_submit(struct dma_async_tx_descriptor *desc)
+
+ This returns a cookie can be used to check the progress of DMA engine
+ activity via other DMA engine calls not covered in this document.
+
+ dmaengine_submit() will not start the DMA operation, it merely adds
+ it to the pending queue. For this, see step 5, dma_async_issue_pending.
+
+5. Issue pending DMA requests and wait for callback notification
+
+ The transactions in the pending queue can be activated by calling the
+ issue_pending API. If channel is idle then the first transaction in
+ queue is started and subsequent ones queued up.
+
+ On completion of each DMA operation, the next in queue is started and
+ a tasklet triggered. The tasklet will then call the client driver
+ completion callback routine for notification, if set.
+
+ Interface:
+
+ .. code-block:: c
+
+ void dma_async_issue_pending(struct dma_chan *chan);
+
+Further APIs:
+-------------
+
+1. Terminate APIs
+
+ .. code-block:: c
+
+ int dmaengine_terminate_sync(struct dma_chan *chan)
+ int dmaengine_terminate_async(struct dma_chan *chan)
+ int dmaengine_terminate_all(struct dma_chan *chan) /* DEPRECATED */
+
+ This causes all activity for the DMA channel to be stopped, and may
+ discard data in the DMA FIFO which hasn't been fully transferred.
+ No callback functions will be called for any incomplete transfers.
+
+ Two variants of this function are available.
+
+ dmaengine_terminate_async() might not wait until the DMA has been fully
+ stopped or until any running complete callbacks have finished. But it is
+ possible to call dmaengine_terminate_async() from atomic context or from
+ within a complete callback. dmaengine_synchronize() must be called before it
+ is safe to free the memory accessed by the DMA transfer or free resources
+ accessed from within the complete callback.
+
+ dmaengine_terminate_sync() will wait for the transfer and any running
+ complete callbacks to finish before it returns. But the function must not be
+ called from atomic context or from within a complete callback.
+
+ dmaengine_terminate_all() is deprecated and should not be used in new code.
+
+2. Pause API
+
+ .. code-block:: c
+
+ int dmaengine_pause(struct dma_chan *chan)
+
+ This pauses activity on the DMA channel without data loss.
+
+3. Resume API
+
+ .. code-block:: c
+
+ int dmaengine_resume(struct dma_chan *chan)
+
+ Resume a previously paused DMA channel. It is invalid to resume a
+ channel which is not currently paused.
+
+4. Check Txn complete
+
+ .. code-block:: c
+
+ enum dma_status dma_async_is_tx_complete(struct dma_chan *chan,
+ dma_cookie_t cookie, dma_cookie_t *last, dma_cookie_t *used)
+
+ This can be used to check the status of the channel. Please see
+ the documentation in include/linux/dmaengine.h for a more complete
+ description of this API.
+
+ This can be used in conjunction with dma_async_is_complete() and
+ the cookie returned from dmaengine_submit() to check for
+ completion of a specific DMA transaction.
+
+ .. note::
+
+ Not all DMA engine drivers can return reliable information for
+ a running DMA channel. It is recommended that DMA engine users
+ pause or stop (via dmaengine_terminate_all()) the channel before
+ using this API.
+
+5. Synchronize termination API
+
+ .. code-block:: c
+
+ void dmaengine_synchronize(struct dma_chan *chan)
+
+ Synchronize the termination of the DMA channel to the current context.
+
+ This function should be used after dmaengine_terminate_async() to synchronize
+ the termination of the DMA channel to the current context. The function will
+ wait for the transfer and any running complete callbacks to finish before it
+ returns.
+
+ If dmaengine_terminate_async() is used to stop the DMA channel this function
+ must be called before it is safe to free memory accessed by previously
+ submitted descriptors or to free any resources accessed within the complete
+ callback of previously submitted descriptors.
+
+ The behavior of this function is undefined if dma_async_issue_pending() has
+ been called between dmaengine_terminate_async() and this function.
diff --git a/Documentation/driver-api/dmaengine/dmatest.rst b/Documentation/driver-api/dmaengine/dmatest.rst
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+==============
+DMA Test Guide
+==============
+
+Andy Shevchenko <andriy.shevchenko@linux.intel.com>
+
+This small document introduces how to test DMA drivers using dmatest module.
+
+.. note::
+ The test suite works only on the channels that have at least one
+ capability of the following: DMA_MEMCPY (memory-to-memory), DMA_MEMSET
+ (const-to-memory or memory-to-memory, when emulated), DMA_XOR, DMA_PQ.
+
+Part 1 - How to build the test module
+=====================================
+
+The menuconfig contains an option that could be found by following path:
+
+ Device Drivers -> DMA Engine support -> DMA Test client
+
+In the configuration file the option called CONFIG_DMATEST. The dmatest could
+be built as module or inside kernel. Let's consider those cases.
+
+Part 2 - When dmatest is built as a module
+==========================================
+
+Example of usage::
+
+ % modprobe dmatest channel=dma0chan0 timeout=2000 iterations=1 run=1
+
+...or::
+
+ % modprobe dmatest
+ % echo dma0chan0 > /sys/module/dmatest/parameters/channel
+ % echo 2000 > /sys/module/dmatest/parameters/timeout
+ % echo 1 > /sys/module/dmatest/parameters/iterations
+ % echo 1 > /sys/module/dmatest/parameters/run
+
+...or on the kernel command line::
+
+ dmatest.channel=dma0chan0 dmatest.timeout=2000 dmatest.iterations=1 dmatest.run=1
+
+.. hint::
+ available channel list could be extracted by running the following command::
+
+ % ls -1 /sys/class/dma/
+
+Once started a message like "dmatest: Started 1 threads using dma0chan0" is
+emitted. After that only test failure messages are reported until the test
+stops.
+
+Note that running a new test will not stop any in progress test.
+
+The following command returns the state of the test. ::
+
+ % cat /sys/module/dmatest/parameters/run
+
+To wait for test completion userpace can poll 'run' until it is false, or use
+the wait parameter. Specifying 'wait=1' when loading the module causes module
+initialization to pause until a test run has completed, while reading
+/sys/module/dmatest/parameters/wait waits for any running test to complete
+before returning. For example, the following scripts wait for 42 tests
+to complete before exiting. Note that if 'iterations' is set to 'infinite' then
+waiting is disabled.
+
+Example::
+
+ % modprobe dmatest run=1 iterations=42 wait=1
+ % modprobe -r dmatest
+
+...or::
+
+ % modprobe dmatest run=1 iterations=42
+ % cat /sys/module/dmatest/parameters/wait
+ % modprobe -r dmatest
+
+Part 3 - When built-in in the kernel
+====================================
+
+The module parameters that is supplied to the kernel command line will be used
+for the first performed test. After user gets a control, the test could be
+re-run with the same or different parameters. For the details see the above
+section `Part 2 - When dmatest is built as a module`_.
+
+In both cases the module parameters are used as the actual values for the test
+case. You always could check them at run-time by running ::
+
+ % grep -H . /sys/module/dmatest/parameters/*
+
+Part 4 - Gathering the test results
+===================================
+
+Test results are printed to the kernel log buffer with the format::
+
+ "dmatest: result <channel>: <test id>: '<error msg>' with src_off=<val> dst_off=<val> len=<val> (<err code>)"
+
+Example of output::
+
+ % dmesg | tail -n 1
+ dmatest: result dma0chan0-copy0: #1: No errors with src_off=0x7bf dst_off=0x8ad len=0x3fea (0)
+
+The message format is unified across the different types of errors. A
+number in the parentheses represents additional information, e.g. error
+code, error counter, or status. A test thread also emits a summary line at
+completion listing the number of tests executed, number that failed, and a
+result code.
+
+Example::
+
+ % dmesg | tail -n 1
+ dmatest: dma0chan0-copy0: summary 1 test, 0 failures 1000 iops 100000 KB/s (0)
+
+The details of a data miscompare error are also emitted, but do not follow the
+above format.
diff --git a/Documentation/driver-api/dmaengine/index.rst b/Documentation/driver-api/dmaengine/index.rst
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+=======================
+DMAEngine documentation
+=======================
+
+DMAEngine documentation provides documents for various aspects of DMAEngine
+framework.
+
+DMAEngine documentation
+-----------------------
+
+This book helps with DMAengine internal APIs and guide for DMAEngine device
+driver writers.
+
+.. toctree::
+ :maxdepth: 1
+
+ provider
+
+DMAEngine client documentation
+------------------------------
+
+This book is a guide to device driver writers on how to use the Slave-DMA
+API of the DMAEngine. This is applicable only for slave DMA usage only.
+
+.. toctree::
+ :maxdepth: 1
+
+ client
+
+DMA Test documentation
+----------------------
+
+This book introduces how to test DMA drivers using dmatest module.
+
+.. toctree::
+ :maxdepth: 1
+
+ dmatest
+
+PXA DMA documentation
+----------------------
+
+This book adds some notes about PXA DMA
+
+.. toctree::
+ :maxdepth: 1
+
+ pxa_dma
+
+.. only:: subproject
+
+ Indices
+ =======
+
+ * :ref:`genindex`
diff --git a/Documentation/driver-api/dmaengine/provider.rst b/Documentation/driver-api/dmaengine/provider.rst
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+==================================
+DMAengine controller documentation
+==================================
+
+Hardware Introduction
+=====================
+
+Most of the Slave DMA controllers have the same general principles of
+operations.
+
+They have a given number of channels to use for the DMA transfers, and
+a given number of requests lines.
+
+Requests and channels are pretty much orthogonal. Channels can be used
+to serve several to any requests. To simplify, channels are the
+entities that will be doing the copy, and requests what endpoints are
+involved.
+
+The request lines actually correspond to physical lines going from the
+DMA-eligible devices to the controller itself. Whenever the device
+will want to start a transfer, it will assert a DMA request (DRQ) by
+asserting that request line.
+
+A very simple DMA controller would only take into account a single
+parameter: the transfer size. At each clock cycle, it would transfer a
+byte of data from one buffer to another, until the transfer size has
+been reached.
+
+That wouldn't work well in the real world, since slave devices might
+require a specific number of bits to be transferred in a single
+cycle. For example, we may want to transfer as much data as the
+physical bus allows to maximize performances when doing a simple
+memory copy operation, but our audio device could have a narrower FIFO
+that requires data to be written exactly 16 or 24 bits at a time. This
+is why most if not all of the DMA controllers can adjust this, using a
+parameter called the transfer width.
+
+Moreover, some DMA controllers, whenever the RAM is used as a source
+or destination, can group the reads or writes in memory into a buffer,
+so instead of having a lot of small memory accesses, which is not
+really efficient, you'll get several bigger transfers. This is done
+using a parameter called the burst size, that defines how many single
+reads/writes it's allowed to do without the controller splitting the
+transfer into smaller sub-transfers.
+
+Our theoretical DMA controller would then only be able to do transfers
+that involve a single contiguous block of data. However, some of the
+transfers we usually have are not, and want to copy data from
+non-contiguous buffers to a contiguous buffer, which is called
+scatter-gather.
+
+DMAEngine, at least for mem2dev transfers, require support for
+scatter-gather. So we're left with two cases here: either we have a
+quite simple DMA controller that doesn't support it, and we'll have to
+implement it in software, or we have a more advanced DMA controller,
+that implements in hardware scatter-gather.
+
+The latter are usually programmed using a collection of chunks to
+transfer, and whenever the transfer is started, the controller will go
+over that collection, doing whatever we programmed there.
+
+This collection is usually either a table or a linked list. You will
+then push either the address of the table and its number of elements,
+or the first item of the list to one channel of the DMA controller,
+and whenever a DRQ will be asserted, it will go through the collection
+to know where to fetch the data from.
+
+Either way, the format of this collection is completely dependent on
+your hardware. Each DMA controller will require a different structure,
+but all of them will require, for every chunk, at least the source and
+destination addresses, whether it should increment these addresses or
+not and the three parameters we saw earlier: the burst size, the
+transfer width and the transfer size.
+
+The one last thing is that usually, slave devices won't issue DRQ by
+default, and you have to enable this in your slave device driver first
+whenever you're willing to use DMA.
+
+These were just the general memory-to-memory (also called mem2mem) or
+memory-to-device (mem2dev) kind of transfers. Most devices often
+support other kind of transfers or memory operations that dmaengine
+support and will be detailed later in this document.
+
+DMA Support in Linux
+====================
+
+Historically, DMA controller drivers have been implemented using the
+async TX API, to offload operations such as memory copy, XOR,
+cryptography, etc., basically any memory to memory operation.
+
+Over time, the need for memory to device transfers arose, and
+dmaengine was extended. Nowadays, the async TX API is written as a
+layer on top of dmaengine, and acts as a client. Still, dmaengine
+accommodates that API in some cases, and made some design choices to
+ensure that it stayed compatible.
+
+For more information on the Async TX API, please look the relevant
+documentation file in Documentation/crypto/async-tx-api.txt.
+
+DMAEngine APIs
+==============
+
+``struct dma_device`` Initialization
+------------------------------------
+
+Just like any other kernel framework, the whole DMAEngine registration
+relies on the driver filling a structure and registering against the
+framework. In our case, that structure is dma_device.
+
+The first thing you need to do in your driver is to allocate this
+structure. Any of the usual memory allocators will do, but you'll also
+need to initialize a few fields in there:
+
+- ``channels``: should be initialized as a list using the
+ INIT_LIST_HEAD macro for example
+
+- ``src_addr_widths``:
+ should contain a bitmask of the supported source transfer width
+
+- ``dst_addr_widths``:
+ should contain a bitmask of the supported destination transfer width
+
+- ``directions``:
+ should contain a bitmask of the supported slave directions
+ (i.e. excluding mem2mem transfers)
+
+- ``residue_granularity``:
+ granularity of the transfer residue reported to dma_set_residue.
+ This can be either:
+
+ - Descriptor:
+ your device doesn't support any kind of residue
+ reporting. The framework will only know that a particular
+ transaction descriptor is done.
+
+ - Segment:
+ your device is able to report which chunks have been transferred
+
+ - Burst:
+ your device is able to report which burst have been transferred
+
+- ``dev``: should hold the pointer to the ``struct device`` associated
+ to your current driver instance.
+
+Supported transaction types
+---------------------------
+
+The next thing you need is to set which transaction types your device
+(and driver) supports.
+
+Our ``dma_device structure`` has a field called cap_mask that holds the
+various types of transaction supported, and you need to modify this
+mask using the dma_cap_set function, with various flags depending on
+transaction types you support as an argument.
+
+All those capabilities are defined in the ``dma_transaction_type enum``,
+in ``include/linux/dmaengine.h``
+
+Currently, the types available are:
+
+- DMA_MEMCPY
+
+ - The device is able to do memory to memory copies
+
+- DMA_XOR
+
+ - The device is able to perform XOR operations on memory areas
+
+ - Used to accelerate XOR intensive tasks, such as RAID5
+
+- DMA_XOR_VAL
+
+ - The device is able to perform parity check using the XOR
+ algorithm against a memory buffer.
+
+- DMA_PQ
+
+ - The device is able to perform RAID6 P+Q computations, P being a
+ simple XOR, and Q being a Reed-Solomon algorithm.
+
+- DMA_PQ_VAL
+
+ - The device is able to perform parity check using RAID6 P+Q
+ algorithm against a memory buffer.
+
+- DMA_INTERRUPT
+
+ - The device is able to trigger a dummy transfer that will
+ generate periodic interrupts
+
+ - Used by the client drivers to register a callback that will be
+ called on a regular basis through the DMA controller interrupt
+
+- DMA_PRIVATE
+
+ - The devices only supports slave transfers, and as such isn't
+ available for async transfers.
+
+- DMA_ASYNC_TX
+
+ - Must not be set by the device, and will be set by the framework
+ if needed
+
+ - TODO: What is it about?
+
+- DMA_SLAVE
+
+ - The device can handle device to memory transfers, including
+ scatter-gather transfers.
+
+ - While in the mem2mem case we were having two distinct types to
+ deal with a single chunk to copy or a collection of them, here,
+ we just have a single transaction type that is supposed to
+ handle both.
+
+ - If you want to transfer a single contiguous memory buffer,
+ simply build a scatter list with only one item.
+
+- DMA_CYCLIC
+
+ - The device can handle cyclic transfers.
+
+ - A cyclic transfer is a transfer where the chunk collection will
+ loop over itself, with the last item pointing to the first.
+
+ - It's usually used for audio transfers, where you want to operate
+ on a single ring buffer that you will fill with your audio data.
+
+- DMA_INTERLEAVE
+
+ - The device supports interleaved transfer.
+
+ - These transfers can transfer data from a non-contiguous buffer
+ to a non-contiguous buffer, opposed to DMA_SLAVE that can
+ transfer data from a non-contiguous data set to a continuous
+ destination buffer.
+
+ - It's usually used for 2d content transfers, in which case you
+ want to transfer a portion of uncompressed data directly to the
+ display to print it
+
+These various types will also affect how the source and destination
+addresses change over time.
+
+Addresses pointing to RAM are typically incremented (or decremented)
+after each transfer. In case of a ring buffer, they may loop
+(DMA_CYCLIC). Addresses pointing to a device's register (e.g. a FIFO)
+are typically fixed.
+
+Device operations
+-----------------
+
+Our dma_device structure also requires a few function pointers in
+order to implement the actual logic, now that we described what
+operations we were able to perform.
+
+The functions that we have to fill in there, and hence have to
+implement, obviously depend on the transaction types you reported as
+supported.
+
+- ``device_alloc_chan_resources``
+
+- ``device_free_chan_resources``
+
+ - These functions will be called whenever a driver will call
+ ``dma_request_channel`` or ``dma_release_channel`` for the first/last
+ time on the channel associated to that driver.
+
+ - They are in charge of allocating/freeing all the needed
+ resources in order for that channel to be useful for your driver.
+
+ - These functions can sleep.
+
+- ``device_prep_dma_*``
+
+ - These functions are matching the capabilities you registered
+ previously.
+
+ - These functions all take the buffer or the scatterlist relevant
+ for the transfer being prepared, and should create a hardware
+ descriptor or a list of hardware descriptors from it
+
+ - These functions can be called from an interrupt context
+
+ - Any allocation you might do should be using the GFP_NOWAIT
+ flag, in order not to potentially sleep, but without depleting
+ the emergency pool either.
+
+ - Drivers should try to pre-allocate any memory they might need
+ during the transfer setup at probe time to avoid putting to
+ much pressure on the nowait allocator.
+
+ - It should return a unique instance of the
+ ``dma_async_tx_descriptor structure``, that further represents this
+ particular transfer.
+
+ - This structure can be initialized using the function
+ ``dma_async_tx_descriptor_init``.
+
+ - You'll also need to set two fields in this structure:
+
+ - flags:
+ TODO: Can it be modified by the driver itself, or
+ should it be always the flags passed in the arguments
+
+ - tx_submit: A pointer to a function you have to implement,
+ that is supposed to push the current transaction descriptor to a
+ pending queue, waiting for issue_pending to be called.
+
+ - In this structure the function pointer callback_result can be
+ initialized in order for the submitter to be notified that a
+ transaction has completed. In the earlier code the function pointer
+ callback has been used. However it does not provide any status to the
+ transaction and will be deprecated. The result structure defined as
+ ``dmaengine_result`` that is passed in to callback_result
+ has two fields:
+
+ - result: This provides the transfer result defined by
+ ``dmaengine_tx_result``. Either success or some error condition.
+
+ - residue: Provides the residue bytes of the transfer for those that
+ support residue.
+
+- ``device_issue_pending``
+
+ - Takes the first transaction descriptor in the pending queue,
+ and starts the transfer. Whenever that transfer is done, it
+ should move to the next transaction in the list.
+
+ - This function can be called in an interrupt context
+
+- ``device_tx_status``
+
+ - Should report the bytes left to go over on the given channel
+
+ - Should only care about the transaction descriptor passed as
+ argument, not the currently active one on a given channel
+
+ - The tx_state argument might be NULL
+
+ - Should use dma_set_residue to report it
+
+ - In the case of a cyclic transfer, it should only take into
+ account the current period.
+
+ - This function can be called in an interrupt context.
+
+- device_config
+
+ - Reconfigures the channel with the configuration given as argument
+
+ - This command should NOT perform synchronously, or on any
+ currently queued transfers, but only on subsequent ones
+
+ - In this case, the function will receive a ``dma_slave_config``
+ structure pointer as an argument, that will detail which
+ configuration to use.
+
+ - Even though that structure contains a direction field, this
+ field is deprecated in favor of the direction argument given to
+ the prep_* functions
+
+ - This call is mandatory for slave operations only. This should NOT be
+ set or expected to be set for memcpy operations.
+ If a driver support both, it should use this call for slave
+ operations only and not for memcpy ones.
+
+- device_pause
+
+ - Pauses a transfer on the channel
+
+ - This command should operate synchronously on the channel,
+ pausing right away the work of the given channel
+
+- device_resume
+
+ - Resumes a transfer on the channel
+
+ - This command should operate synchronously on the channel,
+ resuming right away the work of the given channel
+
+- device_terminate_all
+
+ - Aborts all the pending and ongoing transfers on the channel
+
+ - For aborted transfers the complete callback should not be called
+
+ - Can be called from atomic context or from within a complete
+ callback of a descriptor. Must not sleep. Drivers must be able
+ to handle this correctly.
+
+ - Termination may be asynchronous. The driver does not have to
+ wait until the currently active transfer has completely stopped.
+ See device_synchronize.
+
+- device_synchronize
+
+ - Must synchronize the termination of a channel to the current
+ context.
+
+ - Must make sure that memory for previously submitted
+ descriptors is no longer accessed by the DMA controller.
+
+ - Must make sure that all complete callbacks for previously
+ submitted descriptors have finished running and none are
+ scheduled to run.
+
+ - May sleep.
+
+
+Misc notes
+==========
+
+(stuff that should be documented, but don't really know
+where to put them)
+
+``dma_run_dependencies``
+
+- Should be called at the end of an async TX transfer, and can be
+ ignored in the slave transfers case.
+
+- Makes sure that dependent operations are run before marking it
+ as complete.
+
+dma_cookie_t
+
+- it's a DMA transaction ID that will increment over time.
+
+- Not really relevant any more since the introduction of ``virt-dma``
+ that abstracts it away.
+
+DMA_CTRL_ACK
+
+- If clear, the descriptor cannot be reused by provider until the
+ client acknowledges receipt, i.e. has has a chance to establish any
+ dependency chains
+
+- This can be acked by invoking async_tx_ack()
+
+- If set, does not mean descriptor can be reused
+
+DMA_CTRL_REUSE
+
+- If set, the descriptor can be reused after being completed. It should
+ not be freed by provider if this flag is set.
+
+- The descriptor should be prepared for reuse by invoking
+ ``dmaengine_desc_set_reuse()`` which will set DMA_CTRL_REUSE.
+
+- ``dmaengine_desc_set_reuse()`` will succeed only when channel support
+ reusable descriptor as exhibited by capabilities
+
+- As a consequence, if a device driver wants to skip the
+ ``dma_map_sg()`` and ``dma_unmap_sg()`` in between 2 transfers,
+ because the DMA'd data wasn't used, it can resubmit the transfer right after
+ its completion.
+
+- Descriptor can be freed in few ways
+
+ - Clearing DMA_CTRL_REUSE by invoking
+ ``dmaengine_desc_clear_reuse()`` and submitting for last txn
+
+ - Explicitly invoking ``dmaengine_desc_free()``, this can succeed only
+ when DMA_CTRL_REUSE is already set
+
+ - Terminating the channel
+
+- DMA_PREP_CMD
+
+ - If set, the client driver tells DMA controller that passed data in DMA
+ API is command data.
+
+ - Interpretation of command data is DMA controller specific. It can be
+ used for issuing commands to other peripherals/register reads/register
+ writes for which the descriptor should be in different format from
+ normal data descriptors.
+
+General Design Notes
+====================
+
+Most of the DMAEngine drivers you'll see are based on a similar design
+that handles the end of transfer interrupts in the handler, but defer
+most work to a tasklet, including the start of a new transfer whenever
+the previous transfer ended.
+
+This is a rather inefficient design though, because the inter-transfer
+latency will be not only the interrupt latency, but also the
+scheduling latency of the tasklet, which will leave the channel idle
+in between, which will slow down the global transfer rate.
+
+You should avoid this kind of practice, and instead of electing a new
+transfer in your tasklet, move that part to the interrupt handler in
+order to have a shorter idle window (that we can't really avoid
+anyway).
+
+Glossary
+========
+
+- Burst: A number of consecutive read or write operations that
+ can be queued to buffers before being flushed to memory.
+
+- Chunk: A contiguous collection of bursts
+
+- Transfer: A collection of chunks (be it contiguous or not)
diff --git a/Documentation/driver-api/dmaengine/pxa_dma.rst b/Documentation/driver-api/dmaengine/pxa_dma.rst
new file mode 100644
index 0000000..442ee69
--- /dev/null
+++ b/Documentation/driver-api/dmaengine/pxa_dma.rst
@@ -0,0 +1,190 @@
+==============================
+PXA/MMP - DMA Slave controller
+==============================
+
+Constraints
+===========
+
+a) Transfers hot queuing
+A driver submitting a transfer and issuing it should be granted the transfer
+is queued even on a running DMA channel.
+This implies that the queuing doesn't wait for the previous transfer end,
+and that the descriptor chaining is not only done in the irq/tasklet code
+triggered by the end of the transfer.
+A transfer which is submitted and issued on a phy doesn't wait for a phy to
+stop and restart, but is submitted on a "running channel". The other
+drivers, especially mmp_pdma waited for the phy to stop before relaunching
+a new transfer.
+
+b) All transfers having asked for confirmation should be signaled
+Any issued transfer with DMA_PREP_INTERRUPT should trigger a callback call.
+This implies that even if an irq/tasklet is triggered by end of tx1, but
+at the time of irq/dma tx2 is already finished, tx1->complete() and
+tx2->complete() should be called.
+
+c) Channel running state
+A driver should be able to query if a channel is running or not. For the
+multimedia case, such as video capture, if a transfer is submitted and then
+a check of the DMA channel reports a "stopped channel", the transfer should
+not be issued until the next "start of frame interrupt", hence the need to
+know if a channel is in running or stopped state.
+
+d) Bandwidth guarantee
+The PXA architecture has 4 levels of DMAs priorities : high, normal, low.
+The high priorities get twice as much bandwidth as the normal, which get twice
+as much as the low priorities.
+A driver should be able to request a priority, especially the real-time
+ones such as pxa_camera with (big) throughputs.
+
+Design
+======
+a) Virtual channels
+Same concept as in sa11x0 driver, ie. a driver was assigned a "virtual
+channel" linked to the requestor line, and the physical DMA channel is
+assigned on the fly when the transfer is issued.
+
+b) Transfer anatomy for a scatter-gather transfer
+
+::
+
+ +------------+-----+---------------+----------------+-----------------+
+ | desc-sg[0] | ... | desc-sg[last] | status updater | finisher/linker |
+ +------------+-----+---------------+----------------+-----------------+
+
+This structure is pointed by dma->sg_cpu.
+The descriptors are used as follows :
+
+ - desc-sg[i]: i-th descriptor, transferring the i-th sg
+ element to the video buffer scatter gather
+
+ - status updater
+ Transfers a single u32 to a well known dma coherent memory to leave
+ a trace that this transfer is done. The "well known" is unique per
+ physical channel, meaning that a read of this value will tell which
+ is the last finished transfer at that point in time.
+
+ - finisher: has ddadr=DADDR_STOP, dcmd=ENDIRQEN
+
+ - linker: has ddadr= desc-sg[0] of next transfer, dcmd=0
+
+c) Transfers hot-chaining
+Suppose the running chain is:
+
+::
+
+ Buffer 1 Buffer 2
+ +---------+----+---+ +----+----+----+---+
+ | d0 | .. | dN | l | | d0 | .. | dN | f |
+ +---------+----+-|-+ ^----+----+----+---+
+ | |
+ +----+
+
+After a call to dmaengine_submit(b3), the chain will look like:
+
+::
+
+ Buffer 1 Buffer 2 Buffer 3
+ +---------+----+---+ +----+----+----+---+ +----+----+----+---+
+ | d0 | .. | dN | l | | d0 | .. | dN | l | | d0 | .. | dN | f |
+ +---------+----+-|-+ ^----+----+----+-|-+ ^----+----+----+---+
+ | | | |
+ +----+ +----+
+ new_link
+
+If while new_link was created the DMA channel stopped, it is _not_
+restarted. Hot-chaining doesn't break the assumption that
+dma_async_issue_pending() is to be used to ensure the transfer is actually started.
+
+One exception to this rule :
+
+- if Buffer1 and Buffer2 had all their addresses 8 bytes aligned
+
+- and if Buffer3 has at least one address not 4 bytes aligned
+
+- then hot-chaining cannot happen, as the channel must be stopped, the
+ "align bit" must be set, and the channel restarted As a consequence,
+ such a transfer tx_submit() will be queued on the submitted queue, and
+ this specific case if the DMA is already running in aligned mode.
+
+d) Transfers completion updater
+Each time a transfer is completed on a channel, an interrupt might be
+generated or not, up to the client's request. But in each case, the last
+descriptor of a transfer, the "status updater", will write the latest
+transfer being completed into the physical channel's completion mark.
+
+This will speed up residue calculation, for large transfers such as video
+buffers which hold around 6k descriptors or more. This also allows without
+any lock to find out what is the latest completed transfer in a running
+DMA chain.
+
+e) Transfers completion, irq and tasklet
+When a transfer flagged as "DMA_PREP_INTERRUPT" is finished, the dma irq
+is raised. Upon this interrupt, a tasklet is scheduled for the physical
+channel.
+
+The tasklet is responsible for :
+
+- reading the physical channel last updater mark
+
+- calling all the transfer callbacks of finished transfers, based on
+ that mark, and each transfer flags.
+
+If a transfer is completed while this handling is done, a dma irq will
+be raised, and the tasklet will be scheduled once again, having a new
+updater mark.
+
+f) Residue
+Residue granularity will be descriptor based. The issued but not completed
+transfers will be scanned for all of their descriptors against the
+currently running descriptor.
+
+g) Most complicated case of driver's tx queues
+The most tricky situation is when :
+
+ - there are not "acked" transfers (tx0)
+
+ - a driver submitted an aligned tx1, not chained
+
+ - a driver submitted an aligned tx2 => tx2 is cold chained to tx1
+
+ - a driver issued tx1+tx2 => channel is running in aligned mode
+
+ - a driver submitted an aligned tx3 => tx3 is hot-chained
+
+ - a driver submitted an unaligned tx4 => tx4 is put in submitted queue,
+ not chained
+
+ - a driver issued tx4 => tx4 is put in issued queue, not chained
+
+ - a driver submitted an aligned tx5 => tx5 is put in submitted queue, not
+ chained
+
+ - a driver submitted an aligned tx6 => tx6 is put in submitted queue,
+ cold chained to tx5
+
+ This translates into (after tx4 is issued) :
+
+ - issued queue
+
+ ::
+
+ +-----+ +-----+ +-----+ +-----+
+ | tx1 | | tx2 | | tx3 | | tx4 |
+ +---|-+ ^---|-+ ^-----+ +-----+
+ | | | |
+ +---+ +---+
+ - submitted queue
+ +-----+ +-----+
+ | tx5 | | tx6 |
+ +---|-+ ^-----+
+ | |
+ +---+
+
+- completed queue : empty
+
+- allocated queue : tx0
+
+It should be noted that after tx3 is completed, the channel is stopped, and
+restarted in "unaligned mode" to handle tx4.
+
+Author: Robert Jarzmik <robert.jarzmik@free.fr>