diff options
Diffstat (limited to 'samples/kfifo/dma-example.c')
| -rw-r--r-- | samples/kfifo/dma-example.c | 120 |
1 files changed, 74 insertions, 46 deletions
diff --git a/samples/kfifo/dma-example.c b/samples/kfifo/dma-example.c index b9482c28b41a..06473791c08a 100644 --- a/samples/kfifo/dma-example.c +++ b/samples/kfifo/dma-example.c @@ -24,13 +24,14 @@ 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_ERR "error kfifo_alloc\n"); - return 1; + printk(KERN_WARNING "error kfifo_alloc\n"); + return -ENOMEM; } printk(KERN_INFO "queue size: %u\n", kfifo_size(&fifo)); @@ -41,72 +42,99 @@ static int __init example_init(void) kfifo_put(&fifo, &i); /* kick away first byte */ - ret = kfifo_get(&fifo, &i); + kfifo_skip(&fifo); printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo)); - ret = kfifo_dma_in_prepare(&fifo, sg, ARRAY_SIZE(sg), FIFO_SIZE); - printk(KERN_INFO "DMA sgl entries: %d\n", ret); + /* + * 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_link 0x%.8lx offset 0x%.8x length 0x%.8x\n", + i, sg[i].page_link, sg[i].offset, sg[i].length); - /* if 0 was returned, fifo is full and no sgl was created */ - if (ret) { - printk(KERN_INFO "scatterlist for receive:\n"); - for (i = 0; i < ARRAY_SIZE(sg); i++) { - printk(KERN_INFO - "sg[%d] -> " - "page_link 0x%.8lx offset 0x%.8x length 0x%.8x\n", - i, sg[i].page_link, sg[i].offset, sg[i].length); + if (sg_is_last(&sg[i])) + break; + } - if (sg_is_last(&sg[i])) - break; - } + /* put here your code to setup and exectute the dma operation */ + /* ... */ - /* but here your code to setup and exectute the dma operation */ - /* ... */ + /* example: zero bytes received */ + ret = 0; - /* example: zero bytes received */ - ret = 0; + /* finish the dma operation and update the received data */ + kfifo_dma_in_finish(&fifo, ret); - /* 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; } - ret = kfifo_dma_out_prepare(&fifo, sg, ARRAY_SIZE(sg), 8); - printk(KERN_INFO "DMA sgl entries: %d\n", ret); - - /* if 0 was returned, no data was available and no sgl was created */ - if (ret) { - printk(KERN_INFO "scatterlist for transmit:\n"); - for (i = 0; i < ARRAY_SIZE(sg); i++) { - printk(KERN_INFO - "sg[%d] -> " - "page_link 0x%.8lx offset 0x%.8x length 0x%.8x\n", - i, sg[i].page_link, sg[i].offset, sg[i].length); + printk(KERN_INFO "scatterlist for transmit:\n"); + for (i = 0; i < nents; i++) { + printk(KERN_INFO + "sg[%d] -> " + "page_link 0x%.8lx offset 0x%.8x length 0x%.8x\n", + i, sg[i].page_link, sg[i].offset, sg[i].length); - if (sg_is_last(&sg[i])) - break; - } + if (sg_is_last(&sg[i])) + break; + } - /* but here your code to setup and exectute the dma operation */ - /* ... */ + /* put here your code to setup and exectute the dma operation */ + /* ... */ - /* example: 5 bytes transmitted */ - ret = 5; + /* example: 5 bytes transmitted */ + ret = 5; - /* finish the dma operation and update the transmitted data */ - kfifo_dma_out_finish(&fifo, ret); - } + /* 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) { -#ifdef DYNAMIC - kfifo_free(&test); -#endif + kfifo_free(&fifo); } module_init(example_init); |