linux-kernel - Re: [PATCH] ASoC: mediatek: mt8188: add constraints for PCM

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Message-ID: <8b576880-1c78-84d7-ee46-641c65cdf35d@collabora.com>
Date:   Mon, 3 Jul 2023 14:27:40 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Mark Brown <broonie@...nel.org>,
        Trevor Wu (吳文良) <Trevor.Wu@...iatek.com>
Cc:     "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tiwai@...e.com" <tiwai@...e.com>,
        "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "perex@...ex.cz" <perex@...ex.cz>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>
Subject: Re: [PATCH] ASoC: mediatek: mt8188: add constraints for PCM

Il 30/06/23 13:00, Mark Brown ha scritto:
> On Fri, Jun 30, 2023 at 05:29:23AM +0000, Trevor Wu (吳文良) wrote:
>> On Thu, 2023-06-29 at 16:06 +0100, Mark Brown wrote:
> 
>>> This commit message isn't entirely clear.  The effect of the commit
>>> is
>>> to restrict the configurations supported when using a nau8825 but
>>> it's
>>> not clear what a nau8825 has to do with this or why we're doing this
>>> in
>>> general.  What exactly do you mean when saying that "only a limited
>>> number of parameters are necessary" and what makes this the case?
> 
>> For instance, some userspace frameworks only support specific sampling
>> rates such as 48kHz on Chromebook, making other parameters unnecessary.
>> By restricting the configuration, unexpected usage can be prevented and
>> the alsa_conformance_test process which checks all parameters provided
>> by an ALSA driver can be sped up.
> 
> That's a userspace policy decision, we shouldn't be enforcing this in
> the kernel - even for Chromebooks people can install other OSs on them
> which may make different decisions, and it's always possible that the
> ChromeOS people might change their mind later.  If they're only
> interested in testing 48kHz and it's slowing things down unreasonably
> to test more then they should just only test 48kHz rather than changing
> the driver to work around it.
> 
>> Would it be more beneficial to establish the criteria as a general rule
>> for this machine driver, while limiting the use of the machine driver
>> solely to the Chromebook project? Or do you just suggest that I add
>> more details in the commit messages?
> 
> I think we just shouldn't do this, it's policy for ChromeOS rather than
> something that's actually needed.  If we were doing this it would need a
> much clearer commit message and we should be restricting things to
> Chromebooks only.

I agree with Mark. Except for me it's not a *should not* but a *shall not*.

Such other configurations are supported by the hardware and it is the driver's
duty to support all of them - otherwise I deem the driver to be *incomplete*.
It's then the userspace's duty to properly use the sound APIs and request the
right sampling rate for specific usecases.

Chromebooks aren't special at all in this regard.

Regards,
Angelo