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authorAndre Przywara <andre.przywara@arm.com>2019-12-12 12:00:15 +0000
committerManish Pandey <manish.pandey2@arm.com>2019-12-30 11:40:08 +0000
commitcd50ffd2fcbebc47173174151919333960ebe732 (patch)
treed6578e0431c796f4bfd7629fd8fe2a7796e7bc7a
parent2b4c5e4b6f88cd36055b9881909ffb847570c27a (diff)
downloadtrusted-firmware-a-cd50ffd2fcbebc47173174151919333960ebe732.tar.gz
console: 16550: Prepare for skipping initialisation
On some platforms the UART might have already been initialised, for instance by firmware running before TF-A or by a separate management processor. In this case it would not be need to initialise it again (doing so could create spurious characters). But more importantly this saves us from knowing the right baudrate and the right base clock rate for the UART. This can lead to more robust and versatile firmware builds. Allow to skip the 16550 UART initialisation and baud rate divisor programming, by interpreting an input clock rate of "0" to signify this case. This will just skip the call to console_16550_core_init, but still will register the console properly. Users should just pass 0 as the second parameter, the baudrate (third parameter) will then be ignored as well. Fix copy & paste typos in comments for the console_16550_register() function on the way. Signed-off-by: Andre Przywara <andre.przywara@arm.com> Change-Id: I9f8fca5b358f878fac0f31dc411358fd160786ee
-rw-r--r--drivers/ti/uart/aarch32/16550_console.S18
-rw-r--r--drivers/ti/uart/aarch64/16550_console.S9
-rw-r--r--include/drivers/ti/uart/uart_16550.h5
3 files changed, 26 insertions, 6 deletions
diff --git a/drivers/ti/uart/aarch32/16550_console.S b/drivers/ti/uart/aarch32/16550_console.S
index 692188412f..5cd9b30cd8 100644
--- a/drivers/ti/uart/aarch32/16550_console.S
+++ b/drivers/ti/uart/aarch32/16550_console.S
@@ -89,16 +89,19 @@ endfunc console_16550_core_init
.globl console_16550_register
/* -------------------------------------------------------
- * int console_stm32_register(uintptr_t baseaddr,
+ * int console_16550_register(uintptr_t baseaddr,
* uint32_t clock, uint32_t baud,
- * struct console_stm32 *console);
- * Function to initialize and register a new STM32
+ * console_16550_t *console);
+ * Function to initialize and register a new 16550
* console. Storage passed in for the console struct
* *must* be persistent (i.e. not from the stack).
+ * If r1 (UART clock) is 0, initialisation will be
+ * skipped, relying on previous code to have done
+ * this already. r2 is ignored then as well.
* In: r0 - UART register base address
* r1 - UART clock in Hz
- * r2 - Baud rate
- * r3 - pointer to empty console_stm32 struct
+ * r2 - Baud rate (ignored if r1 is 0)
+ * r3 - pointer to empty console_16550_t struct
* Out: return 1 on success, 0 on error
* Clobber list : r0, r1, r2
* -------------------------------------------------------
@@ -110,10 +113,15 @@ func console_16550_register
beq register_fail
str r0, [r4, #CONSOLE_T_16550_BASE]
+ /* A clock rate of zero means to skip the initialisation. */
+ cmp r1, #0
+ beq register_16550
+
bl console_16550_core_init
cmp r0, #0
beq register_fail
+register_16550:
mov r0, r4
pop {r4, lr}
finish_console_register 16550 putc=1, getc=1, flush=1
diff --git a/drivers/ti/uart/aarch64/16550_console.S b/drivers/ti/uart/aarch64/16550_console.S
index dab46e8c50..80c1b86462 100644
--- a/drivers/ti/uart/aarch64/16550_console.S
+++ b/drivers/ti/uart/aarch64/16550_console.S
@@ -92,9 +92,12 @@ endfunc console_16550_core_init
* Function to initialize and register a new 16550
* console. Storage passed in for the console struct
* *must* be persistent (i.e. not from the stack).
+ * If w1 (UART clock) is 0, initialisation will be
+ * skipped, relying on previous code to have done
+ * this already. w2 is ignored then as well.
* In: x0 - UART register base address
* w1 - UART clock in Hz
- * w2 - Baud rate
+ * w2 - Baud rate (ignored if w1 is 0)
* x3 - pointer to empty console_16550_t struct
* Out: return 1 on success, 0 on error
* Clobber list : x0, x1, x2, x6, x7, x14
@@ -106,9 +109,13 @@ func console_16550_register
cbz x6, register_fail
str x0, [x6, #CONSOLE_T_16550_BASE]
+ /* A clock rate of zero means to skip the initialisation. */
+ cbz w1, register_16550
+
bl console_16550_core_init
cbz x0, register_fail
+register_16550:
mov x0, x6
mov x30, x7
finish_console_register 16550 putc=1, getc=1, flush=1
diff --git a/include/drivers/ti/uart/uart_16550.h b/include/drivers/ti/uart/uart_16550.h
index 32e38f0ac1..2b95fa33a6 100644
--- a/include/drivers/ti/uart/uart_16550.h
+++ b/include/drivers/ti/uart/uart_16550.h
@@ -87,6 +87,11 @@ typedef struct {
* framework. The |console| pointer must point to storage that will be valid
* for the lifetime of the console, such as a global or static local variable.
* Its contents will be reinitialized from scratch.
+ * When |clock| has a value of 0, the UART will *not* be initialised. This
+ * means the UART should already be enabled and the baudrate and clock setup
+ * should have been done already, either by platform specific code or by
+ * previous firmware stages. The |baud| parameter will be ignored in this
+ * case as well.
*/
int console_16550_register(uintptr_t baseaddr, uint32_t clock, uint32_t baud,
console_16550_t *console);