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

From: Dmitry Osipenko <digetx@gmail.com>
To: Mark Brown <broonie@kernel.org>,
	robh+dt@kernel.org, mark.rutland@arm.com
Cc: alsa-devel@alsa-project.org, pgaikwad@nvidia.com,
	lgirdwood@gmail.com, spujar@nvidia.com, mperttunen@nvidia.com,
	thierry.reding@gmail.com, josephl@nvidia.com,
	linux-clk@vger.kernel.org, mmaddireddy@nvidia.com,
	daniel.lezcano@linaro.org, krzk@kernel.org, jonathanh@nvidia.com,
	mturquette@baylibre.com, devicetree@vger.kernel.org,
	arnd@arndb.de, markz@nvidia.com, alexios.zavras@intel.com,
	tiwai@suse.com, linux-tegra@vger.kernel.org,
	horms+renesas@verge.net.au, tglx@linutronix.de,
	allison@lohutok.net, sboyd@kernel.org,
	gregkh@linuxfoundation.org, pdeschrijver@nvidia.com,
	linux-kernel@vger.kernel.org, vidyas@nvidia.com,
	Jisheng.Zhang@synaptics.com,
	Sowjanya Komatineni <skomatineni@nvidia.com>
Subject: Re: [alsa-devel] [PATCH v3 09/15] ASoC: tegra: Add fallback for audio mclk
Date: Tue, 10 Dec 2019 21:24:43 +0300	[thread overview]
Message-ID: <560185d9-32fd-a85e-5feb-105f79b953c6@gmail.com> (raw)
In-Reply-To: <20191209204735.GK5483@sirena.org.uk>

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.
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