[alsa-devel] Something broke in snd_soc_pcm_stream

Timur Tabi timur at freescale.com
Wed Jun 8 00:20:25 CEST 2011

Mark Brown wrote:
> I don't think this is a bug in the core, relying on the having things
> partially initialised in a particular order seems overly fragile -
> better to check for the thing you're actually looking for.  There wasn't
> a deliberate change I can think of here, though.

I think it's because you test the codec_dai in soc_new_pcm(), which seems weird.
 I put some printks in this function, and this is what I got:

soc_new_pcm:2132 codec_dai=e6998840
soc_new_pcm:2133 codec_dai->driver->playback.channels_min=2
soc_new_pcm:2134 codec_dai->driver->capture.channels_min=0
soc_new_pcm:2136 cpu_dai->driver->playback.channels_min=2
soc_new_pcm:2137 cpu_dai->driver->capture.channels_min=2
soc_new_pcm:2144 playback=1
soc_new_pcm:2145 capture=0
soc_new_pcm:2173 platform->driver->pcm_new=c0329fd0
fsl_dma_new:305 dai->driver->playback.channels_min=2
fsl_dma_new:306 dai->driver->capture.channels_min=2
fsl_dma_new:329 pcm=e69aae00
fsl_dma_new:330 pcm->streams[1].substream=  (null)

It just so happens that on the the P1022, the CPU does support both directions
in its DAI, but the codec (WM8776) supports only one direction per DAI.  So I
suspect that you shouldn't be testing codec_dai either, because it assumes that
the codec is the only arbiter on which direction a given dai-group supports.

Anyway, I changed my driver to test for the actual pointer, and it works.  You
might want to consider doing the same in soc_pcm_new().

Timur Tabi
Linux kernel developer at Freescale

More information about the Alsa-devel mailing list