[alsa-devel] Something broke in snd_soc_pcm_stream
Mark,
I'm testing your for-3.1 branch on the P1022DS, and I'm getting a kernel panic because a pointer is NULL where I don't expect it to be. In fsl_dma_new(), I have this code:
if (dai->driver->capture.channels_min) { ret = snd_dma_alloc_pages(SNDRV_DMA_TYPE_DEV, card->dev, fsl_dma_hardware.buffer_bytes_max, &pcm->streams[1].substream->dma_buffer); if (ret) { dev_err(card->dev, "can't alloc capture dma buffer\n"); snd_dma_free_pages(&pcm->streams[0].substream->dma_buffer); return ret; } }
I test for channels_min because the playback stream is registered separately from the capture stream, so I expect fsl_dma_new() to be called twice: once to initialize playback, and again to initialize capture.
In the past, if dai->driver->capture.channels_min was equal to some non-zero value, then pcm->streams[1].substream was also non-NULL. This appears no longer to be true. Now it appears that playback.channels_min and capture.channels_min are both set to 2 before fsl_dma_new() is called the first time.
I can change my code to do this:
if (pcm->streams[1].substream) { ret = snd_dma_alloc_pages(SNDRV_DMA_TYPE_DEV, card->dev, fsl_dma_hardware.buffer_bytes_max, &pcm->streams[1].substream->dma_buffer); if (ret) { dev_err(card->dev, "can't alloc capture dma buffer\n"); snd_dma_free_pages(&pcm->streams[0].substream->dma_buffer); return ret; } }
But before I do that, I'd like to know if this is a bug in ASoC, or just a new behavior that I need to handle.
On Tue, Jun 07, 2011 at 04:31:52PM -0500, Timur Tabi wrote:
I can change my code to do this:
if (pcm->streams[1].substream) {
instead of checking for channels_min.
ret = snd_dma_alloc_pages(SNDRV_DMA_TYPE_DEV, card->dev, fsl_dma_hardware.buffer_bytes_max, &pcm->streams[1].substream->dma_buffer); if (ret) { dev_err(card->dev, "can't alloc capture dma buffer\n"); snd_dma_free_pages(&pcm->streams[0].substream->dma_buffer); return ret; } }
But before I do that, I'd like to know if this is a bug in ASoC, or just a new behavior that I need to handle.
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.
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 soc_new_pcm:2176 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().
On Tue, Jun 07, 2011 at 05:20:25PM -0500, Timur Tabi wrote:
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.
Or it just means that unidirectional CPU DAIs are so rare that nobody got round to adding the check for them.
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().
I know we've been round this loop quite a few times in the past but just to reiterate the situation with Linux is rather different to with other OSs - you can submit patches to *any* code in Linux, you're not restricted to only working on your individual driver.
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Mark Brown -
Timur Tabi