v4.19.13 snapshot.
diff --git a/samples/kfifo/dma-example.c b/samples/kfifo/dma-example.c
new file mode 100644
index 0000000..be0d4a5
--- /dev/null
+++ b/samples/kfifo/dma-example.c
@@ -0,0 +1,143 @@
+/*
+ * Sample fifo dma implementation
+ *
+ * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
+ *
+ * Released under the GPL version 2 only.
+ *
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kfifo.h>
+
+/*
+ * This module shows how to handle fifo dma operations.
+ */
+
+/* fifo size in elements (bytes) */
+#define FIFO_SIZE 32
+
+static struct kfifo fifo;
+
+static int __init example_init(void)
+{
+ int i;
+ unsigned int ret;
+ unsigned int nents;
+ struct scatterlist sg[10];
+
+ printk(KERN_INFO "DMA fifo test start\n");
+
+ if (kfifo_alloc(&fifo, FIFO_SIZE, GFP_KERNEL)) {
+ printk(KERN_WARNING "error kfifo_alloc\n");
+ return -ENOMEM;
+ }
+
+ printk(KERN_INFO "queue size: %u\n", kfifo_size(&fifo));
+
+ kfifo_in(&fifo, "test", 4);
+
+ for (i = 0; i != 9; i++)
+ kfifo_put(&fifo, i);
+
+ /* kick away first byte */
+ kfifo_skip(&fifo);
+
+ printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));
+
+ /*
+ * Configure the kfifo buffer to receive data from DMA input.
+ *
+ * .--------------------------------------.
+ * | 0 | 1 | 2 | ... | 12 | 13 | ... | 31 |
+ * |---|------------------|---------------|
+ * \_/ \________________/ \_____________/
+ * \ \ \
+ * \ \_allocated data \
+ * \_*free space* \_*free space*
+ *
+ * We need two different SG entries: one for the free space area at the
+ * end of the kfifo buffer (19 bytes) and another for the first free
+ * byte at the beginning, after the kfifo_skip().
+ */
+ sg_init_table(sg, ARRAY_SIZE(sg));
+ nents = kfifo_dma_in_prepare(&fifo, sg, ARRAY_SIZE(sg), FIFO_SIZE);
+ printk(KERN_INFO "DMA sgl entries: %d\n", nents);
+ if (!nents) {
+ /* fifo is full and no sgl was created */
+ printk(KERN_WARNING "error kfifo_dma_in_prepare\n");
+ return -EIO;
+ }
+
+ /* receive data */
+ printk(KERN_INFO "scatterlist for receive:\n");
+ for (i = 0; i < nents; i++) {
+ printk(KERN_INFO
+ "sg[%d] -> "
+ "page %p offset 0x%.8x length 0x%.8x\n",
+ i, sg_page(&sg[i]), sg[i].offset, sg[i].length);
+
+ if (sg_is_last(&sg[i]))
+ break;
+ }
+
+ /* put here your code to setup and exectute the dma operation */
+ /* ... */
+
+ /* example: zero bytes received */
+ ret = 0;
+
+ /* finish the dma operation and update the received data */
+ kfifo_dma_in_finish(&fifo, ret);
+
+ /* Prepare to transmit data, example: 8 bytes */
+ nents = kfifo_dma_out_prepare(&fifo, sg, ARRAY_SIZE(sg), 8);
+ printk(KERN_INFO "DMA sgl entries: %d\n", nents);
+ if (!nents) {
+ /* no data was available and no sgl was created */
+ printk(KERN_WARNING "error kfifo_dma_out_prepare\n");
+ return -EIO;
+ }
+
+ printk(KERN_INFO "scatterlist for transmit:\n");
+ for (i = 0; i < nents; i++) {
+ printk(KERN_INFO
+ "sg[%d] -> "
+ "page %p offset 0x%.8x length 0x%.8x\n",
+ i, sg_page(&sg[i]), sg[i].offset, sg[i].length);
+
+ if (sg_is_last(&sg[i]))
+ break;
+ }
+
+ /* put here your code to setup and exectute the dma operation */
+ /* ... */
+
+ /* example: 5 bytes transmitted */
+ ret = 5;
+
+ /* finish the dma operation and update the transmitted data */
+ kfifo_dma_out_finish(&fifo, ret);
+
+ ret = kfifo_len(&fifo);
+ printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));
+
+ if (ret != 7) {
+ printk(KERN_WARNING "size mismatch: test failed");
+ return -EIO;
+ }
+ printk(KERN_INFO "test passed\n");
+
+ return 0;
+}
+
+static void __exit example_exit(void)
+{
+ kfifo_free(&fifo);
+}
+
+module_init(example_init);
+module_exit(example_exit);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");