linux-kernel - Re: ALSA: pcm: use dma_can_mmap() to check if a device supports dma_mmap

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Date:   Mon, 4 Nov 2019 09:49:43 +0100
From:   Greg Kroah-Hartman <gregkh@...gle.com>
To:     youling 257 <youling257@...il.com>, Takashi Iwai <tiwai@...e.de>
Cc:     linux-xtensa@...ux-xtensa.org, Michal Simek <monstr@...str.eu>,
        Vladimir Murzin <vladimir.murzin@....com>,
        linux-parisc@...r.kernel.org, linux-sh@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, Helge Deller <deller@....de>,
        x86@...nel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-m68k@...ts.linux-m68k.org,
        Robin Murphy <robin.murphy@....com>,
        linux-arm-kernel@...ts.infradead.org, hch@....de
Subject: Re: ALSA: pcm: use dma_can_mmap() to check if a device supports
 dma_mmap_*

On 11/4/19 9:32 AM, Greg Kroah-Hartman wrote:
 > On 11/4/19 9:27 AM, youling 257 wrote:
 >  > This driver
 > 
https://android.googlesource.com/kernel/common/+/refs/heads/android-mainline/drivers/usb/gadget/function/f_audio_source.c 

 >
 >  >
 >
 > The driver is broken and needs to be fixed.  Please feel free to submit
 > patches to AOSP to do so as you can trigger this easily.

Hm, maybe the driver isn't broken...

snd_pcm_lib_preallocate_pages_for_all() is called with
SNDRV_DMA_TYPE_DEV set, so that should be fine, and the only other
buffer I can see allocate here is with a call to
snd_pcm_lib_alloc_vmalloc_buffer() which _should_ be ok, right?

I don't see any buffers coming off the stack here, unless the gadget
controller is the one creating them?

thanks,

greg k-h