linux-kernel - Re: [PATCH v3 09/15] ASoC: tegra: Add fallback for audio mclk

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Message-ID: <560185d9-32fd-a85e-5feb-105f79b953c6@gmail.com>
Date:   Tue, 10 Dec 2019 21:24:43 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Mark Brown <broonie@...nel.org>, robh+dt@...nel.org,
        mark.rutland@....com
Cc:     Sowjanya Komatineni <skomatineni@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com,
        mperttunen@...dia.com, gregkh@...uxfoundation.org,
        sboyd@...nel.org, tglx@...utronix.de, allison@...utok.net,
        pdeschrijver@...dia.com, pgaikwad@...dia.com,
        mturquette@...libre.com, horms+renesas@...ge.net.au,
        Jisheng.Zhang@...aptics.com, krzk@...nel.org, arnd@...db.de,
        spujar@...dia.com, josephl@...dia.com, vidyas@...dia.com,
        daniel.lezcano@...aro.org, mmaddireddy@...dia.com,
        markz@...dia.com, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, lgirdwood@...il.com, perex@...ex.cz,
        tiwai@...e.com, alexios.zavras@...el.com,
        alsa-devel@...a-project.org
Subject: Re: [PATCH v3 09/15] ASoC: tegra: Add fallback for audio mclk

09.12.2019 23:47, Mark Brown пишет:
> On Mon, Dec 09, 2019 at 11:31:59PM +0300, Dmitry Osipenko wrote:
>> 09.12.2019 19:40, Mark Brown пишет:
> 
>>> Why would this need to be a stable fix?  Presumably people with stable
>>> kernels are using the old device tree anyway?
> 
>> At least Rob Herring is asking to maintain backwards compatibility
>> because some ditros are using newer device-trees with stable kernels.
> 
> You're talking about forwards compatibility not backwards here.  Are
> those distros actually using LTS kernels?

I think openSUSE Leap could be one of those distros that use LTS kernel
with newer device-trees, but that's not 100%. Maybe Rob could help
clarifying that.

>> I'm personally also tending to use the newer DTB with older kernel
>> version whenever there is a need to check something using stable kernel.
>> Perhaps losing sound is not very important, but will be nicer if that
>> doesn't happen.
> 
> That really does sound like a "you broke it, you get all the pieces"
> situation TBH...  I'd be a lot more comfortable if the stable kernels
> were sticking to bugfix only though I do appreciate that they're not
> really that any more.

In some cases it could be painful to maintain device-tree compatibility
for platforms like NVIDIA Tegra SoCs because hardware wasn't modeled
correctly from the start.

I agree that people should use relevant device-trees. It's quite a lot
of hassle to care about compatibility for platforms that are permanently
in a development state. It could be more reasonable to go through the
pain if kernel required a full-featured device tree for every SoC from
the start.

But maybe Tegra / device-tree maintainers have a different opinion.
IIUC, device-trees are meant to be stable and software-agnostic, at
least that was the case not so long time ago and I don't think that this
premise changed.