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

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Message-ID: <8c3be94e-56c0-4820-853d-669e90969c24@sirena.org.uk>
Date:   Thu, 29 Jun 2023 18:42:57 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.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 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?

> > > 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.

I'm still not clear why you believe this to be a bug.

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