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

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Date:   Fri, 30 Jun 2023 06:42:42 +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 18:42, Mark Brown wrote:
> On Thu, Jun 29, 2023 at 06:33:09PM +0100, Srinivas Kandagatla wrote:
>> 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.
> 
> Why is this an actual problem rather than just being a bit ugly?  What
> is the negative consequence of having a PCM with this number?

Yes, it is ugly but also breaks the existing UCM as the pcm device 
numbers keep changing.
Which is why I refereed it as bug in the driver.

--srini