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SubjectRe: [PATCH 4/7] ALSA: pcm: use dma_can_mmap() to check if a device supports dma_mmap_*
On Mon, 05 Aug 2019 11:11:56 +0200,
Christoph Hellwig wrote:
>
> Replace the local hack with the dma_can_mmap helper to check if
> a given device supports mapping DMA allocations to userspace.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> sound/core/pcm_native.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> index 703857aab00f..81c82c3ee8a2 100644
> --- a/sound/core/pcm_native.c
> +++ b/sound/core/pcm_native.c
> @@ -220,12 +220,11 @@ static bool hw_support_mmap(struct snd_pcm_substream *substream)
> {
> if (!(substream->runtime->hw.info & SNDRV_PCM_INFO_MMAP))
> return false;
> - /* architecture supports dma_mmap_coherent()? */
> -#if defined(CONFIG_ARCH_NO_COHERENT_DMA_MMAP) || !defined(CONFIG_HAS_DMA)
> + if (!dma_can_mmap(substream->dma_buffer.dev.dev))
> + return false;
> if (!substream->ops->mmap &&
> substream->dma_buffer.dev.type == SNDRV_DMA_TYPE_DEV)
> return false;
> -#endif

This won't work as expected, unfortunately. It's a bit tricky check,
since the driver may have its own mmap implementation via
substream->ops->mmap, and the dma_buffer.dev.dev might point to
another object depending on the dma_buffer.dev.type.

So please replace with something like below:

--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -221,11 +221,10 @@ static bool hw_support_mmap(struct snd_pcm_substream *substream)
if (!(substream->runtime->hw.info & SNDRV_PCM_INFO_MMAP))
return false;
/* architecture supports dma_mmap_coherent()? */
-#if defined(CONFIG_ARCH_NO_COHERENT_DMA_MMAP) || !defined(CONFIG_HAS_DMA)
if (!substream->ops->mmap &&
- substream->dma_buffer.dev.type == SNDRV_DMA_TYPE_DEV)
+ substream->dma_buffer.dev.type == SNDRV_DMA_TYPE_DEV &&
+ !dma_can_mmap(substream->dma_buffer.dev.dev))
return false;
-#endif
return true;
}


Thanks!

Takashi

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