Re: ALSA: pcm: use dma_can_mmap() to check if a device supports dma_mmap_*

youling 257 <youling257@xxxxxxxxx> · Mon, 4 Nov 2019 16:27:20 +0800

This driver https://android.googlesource.com/kernel/common/+/refs/heads/android-mainline/drivers/usb/gadget/function/f_audio_source.c

2019-11-04 16:02 GMT+08:00, Takashi Iwai <tiwai@xxxxxxx>:

Exactly which driver is hit?  The code path is via hw_support_mmap()
and it's currently:

static bool hw_support_mmap(struct snd_pcm_substream *substream)
{
	if (!(substream->runtime->hw.info & SNDRV_PCM_INFO_MMAP))
		return false;

	if (substream->ops->mmap ||
	    substream->dma_buffer.dev.type != SNDRV_DMA_TYPE_DEV)
		return true;

	return dma_can_mmap(substream->dma_buffer.dev.dev);
}

so at least the driver has already set the SNDRV_DMA_TYPE_DEV
explicitly (it's non-zero) and some device object, but the device
object was invalid for dma_can_mmap() call.

This smells more like a driver-side issue, not in the core side.

thanks,

Takashi