diff options
| -rw-r--r-- | Documentation/sound/kernel-api/writing-an-alsa-driver.rst | 66 |
1 files changed, 37 insertions, 29 deletions
diff --git a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst index 5385618fd881..ba008ce28029 100644 --- a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst +++ b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst @@ -2095,10 +2095,12 @@ This callback is atomic as default. page callback ~~~~~~~~~~~~~ -This callback is optional too. This callback is used mainly for -non-contiguous buffers. The mmap calls this callback to get the page -address. Some examples will be explained in the later section `Buffer -and Memory Management`_, too. +This callback is optional too. The mmap calls this callback to get the +page fault address. + +Since the recent changes, you need no special callback any longer for +the standard SG-buffer or vmalloc-buffer. Hence this callback should +be rarely used. mmap calllback ~~~~~~~~~~~~~~ @@ -3700,8 +3702,15 @@ For creating the SG-buffer handler, call ``SNDRV_DMA_TYPE_DEV_SG`` in the PCM constructor like other PCI pre-allocator. You need to pass ``snd_dma_pci_data(pci)``, where pci is the :c:type:`struct pci_dev <pci_dev>` pointer of the chip as -well. The ``struct snd_sg_buf`` instance is created as -``substream->dma_private``. You can cast the pointer like: +well. + +:: + + snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV_SG, + snd_dma_pci_data(pci), size, max); + +The ``struct snd_sg_buf`` instance is created as +``substream->dma_private`` in turn. You can cast the pointer like: :: @@ -3717,10 +3726,6 @@ physically non-contiguous. The physical address table is set up in ``sgbuf->table``. You can get the physical address at a certain offset via :c:func:`snd_pcm_sgbuf_get_addr()`. -When a SG-handler is used, you need to set -:c:func:`snd_pcm_sgbuf_ops_page()` as the ``page`` callback. (See -`page callback`_ section.) - To release the data, call :c:func:`snd_pcm_lib_free_pages()` in the ``hw_free`` callback as usual. @@ -3728,30 +3733,33 @@ Vmalloc'ed Buffers ------------------ It's possible to use a buffer allocated via :c:func:`vmalloc()`, for -example, for an intermediate buffer. Since the allocated pages are not -contiguous, you need to set the ``page`` callback to obtain the physical -address at every offset. +example, for an intermediate buffer. In the recent version of kernel, +you can simply allocate it via standard +:c:func:`snd_pcm_lib_malloc_pages()` and co after setting up the +buffer preallocation with ``SNDRV_DMA_TYPE_VMALLOC`` type. -The easiest way to achieve it would be to use -:c:func:`snd_pcm_lib_alloc_vmalloc_buffer()` for allocating the buffer -via :c:func:`vmalloc()`, and set :c:func:`snd_pcm_sgbuf_ops_page()` to -the ``page`` callback. At release, you need to call -:c:func:`snd_pcm_lib_free_vmalloc_buffer()`. +:: -If you want to implementation the ``page`` manually, it would be like -this: + snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_VMALLOC, + NULL, 0, 0); -:: +The NULL is passed to the device pointer argument, which indicates +that the default pages (GFP_KERNEL and GFP_HIGHMEM) will be +allocated. - #include <linux/vmalloc.h> +Also, note that zero is passed to both the size and the max size +arguments here. Since each vmalloc call should succeed at any time, +we don't need to pre-allocate the buffers like other continuous +pages. - /* get the physical page pointer on the given offset */ - static struct page *mychip_page(struct snd_pcm_substream *substream, - unsigned long offset) - { - void *pageptr = substream->runtime->dma_area + offset; - return vmalloc_to_page(pageptr); - } +If you need the 32bit DMA allocation, pass the device pointer encoded +by :c:func:`snd_dma_continuous_data()` with ``GFP_KERNEL|__GFP_DMA32`` +argument. + +:: + + snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_VMALLOC, + snd_dma_continuous_data(GFP_KERNEL | __GFP_DMA32), 0, 0); Proc Interface ============== |