linux-kernel - Re: [PATCH 4/7] ALSA: pcm: use dma_can_mmap() to check if a device supports dma_mmap

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Message-ID: <20190806052949.GC13409@lst.de>
Date:   Tue, 6 Aug 2019 07:29:49 +0200
From:   Christoph Hellwig <hch@....de>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Michal Simek <monstr@...str.eu>,
        linux-arm-kernel@...ts.infradead.org,
        linux-m68k@...ts.linux-m68k.org, linux-parisc@...r.kernel.org,
        linux-sh@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] ALSA: pcm: use dma_can_mmap() to check if a device
 supports dma_mmap_*

On Mon, Aug 05, 2019 at 11:22:03AM +0200, Takashi Iwai wrote:
> 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:

>From my gut feeling I'd reorder it a bit to make it more clear like
this:

http://git.infradead.org/users/hch/misc.git/commitdiff/958fccf54d00c16740522f818d23f9350498e911

if this is fine it'll be in the next version, waiting for a little more
feedback on the other patches.