[alsa-devel] Bug in hdmi codec driver in DPCM

[Patrick Lai]

On 10/30/18 7:50 AM, Rohit Kumar wrote:
> Hi,
> 
> We are facing crash in hdmi codec driver when we use DPCM based 
> dai-links. Crash is happening in hdmi_codec_eld_chmap() while accessing 
> chmap_info struct during hdmi_codec_startup(). However, chmap_info 
> struct is allocated in hdmi_codec_pcm_new() which is only called in 
> non-DPCM based dai-links.
> 
> Below is the crash stack:
> 
> [61.635493] Unable to handle kernel NULL pointer dereference at virtual 
> address 00000018
> 
> .....
> 
> [61.666696]CM = 0, WnR = 1
> 
> [61.669778] user pgtable: 4k pages, 39-bit VAs, pgd = ffffffc0d6633000
> 
> [61.676526] [0000000000000018] *pgd=0000000153fc8003, 
> *pud=0000000153fc8003, *pmd=0000000000000000
> 
> [61.685793] Internal error: Oops: 96000046 [#1] PREEMPT SMP
> 
> [61.722955] CPU: 7 PID: 2238 Comm: aplay Not tainted 4.14.72 #21
> 
> ..
> 
> [61.740269] PC is at hdmi_codec_startup+0x124/0x164
> 
> [61.745308] LR is at hdmi_codec_startup+0xe4/0x164
> 
> ..
> 
> We would probably need to move the implementation on pcm_new() to some 
> other function to make it compatible with DPCM.
> 
> Can you please provide suggestions in solving the issue.
> 
In my opinion, it is not responsibility of driver to speculate whether
the ops it exposes would only be called under certain usage (non-DPCM in
this case). I think ASoC framework should be updated to call pcm_new()
of each driver even though no actual PCM device would be created for
backend dailink.

> 
> Thanks,
> 
> Rohit


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