linux-kernel - Re: [PATCH] ASoC: qdsp6: q6apm: use dai link pcm id as pcm device number

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Date:   Thu, 29 Jun 2023 18:33:09 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     johan+linaro@...nel.org, perex@...ex.cz, tiwai@...e.com,
        lgirdwood@...il.com, ckeepax@...nsource.cirrus.com,
        kuninori.morimoto.gx@...esas.com, linux-kernel@...r.kernel.org,
        pierre-louis.bossart@...ux.intel.com, alsa-devel@...a-project.org,
        Stable@...r.kernel.org
Subject: Re: [PATCH] ASoC: qdsp6: q6apm: use dai link pcm id as pcm device
 number



On 29/06/2023 16:43, Mark Brown wrote:
> On Wed, Jun 28, 2023 at 10:24:04AM +0100, Srinivas Kandagatla wrote:
>> For some reason we ended up with a setup without this flag.
>> This resulted in inconsistent sound card devices numbers which
>>   are also not starting as expected at dai_link->id.
>>   (Ex: MultiMedia1 pcm ended up with device number 4 instead of 0)
> 
> Why is this a problem?

In existing Qualcomm setup the backend pcm are added first, which 
results in frontend pcms getting pcm numbers after this.

For example: with 3 backend dailinks in DT we have frontend pcm start at 
3. Now if we add new backend dai-link in DT we now have frontend pcm 
start at 4.

This is a bug in qualcomm driver.

> 
>> With this patch patch now the MultiMedia1 PCM ends up with device number 0
>> as expected.
>>
>> Fixes: 9b4fe0f1cd79 ("ASoC: qdsp6: audioreach: add q6apm-dai support")
>> Cc: <Stable@...r.kernel.org>
> 
> Won't this be an ABI change?  That seems like it'd disrupt things in
> stable.
Yes, but this is a real bug. without fixing this also results in abi(pcm 
number) change when we add new backend dai-link. I have also sent fix 
for UCM to handle this.


--srini