Re: [PATCH v3 03/15] soc: tegra: Add Tegra PMC clock registrations into PMC driver

From: Peter De Schrijver <pdeschrijver@nvidia.com>
To: Dmitry Osipenko <digetx@gmail.com>
Cc: Sowjanya Komatineni <skomatineni@nvidia.com>,
	<thierry.reding@gmail.com>, <jonathanh@nvidia.com>,
	<mperttunen@nvidia.com>, <sboyd@kernel.org>,
	<gregkh@linuxfoundation.org>, <tglx@linutronix.de>,
	<robh+dt@kernel.org>, <mark.rutland@arm.com>,
	<allison@lohutok.net>, <pgaikwad@nvidia.com>,
	<mturquette@baylibre.com>, <horms+renesas@verge.net.au>,
	<Jisheng.Zhang@synaptics.com>, <krzk@kernel.org>, <arnd@arndb.de>,
	<spujar@nvidia.com>, <josephl@nvidia.com>, <vidyas@nvidia.com>,
	<daniel.lezcano@linaro.org>, <mmaddireddy@nvidia.com>,
	<markz@nvidia.com>, <devicetree@vger.kernel.org>,
	<linux-clk@vger.kernel.org>, <linux-tegra@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>, <lgirdwood@gmail.com>,
	<broonie@kernel.org>, <perex@perex.cz>, <tiwai@suse.com>,
	<alexios.zavras@intel.com>, <alsa-devel@alsa-project.org>
Subject: Re: [PATCH v3 03/15] soc: tegra: Add Tegra PMC clock registrations into PMC driver
Date: Mon, 16 Dec 2019 17:24:35 +0200	[thread overview]
Message-ID: <20191216152435.GD28289@pdeschrijver-desktop.Nvidia.com> (raw)
In-Reply-To: <20191216151132.GC28289@pdeschrijver-desktop.Nvidia.com>

On Mon, Dec 16, 2019 at 05:11:32PM +0200, Peter De Schrijver wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Mon, Dec 16, 2019 at 05:23:23PM +0300, Dmitry Osipenko wrote:
> > >> Could you please clarify what do you mean by the "existing users"?
> > >> AFAIK, nothing in kernel uses mux clocks.
> > >
> > > The DT clk bindings allow for parent initialization, so it's certainly
> > > possible there are some DTs which rely on this. We promised to never
> > > break the bindings, which changing to 1 clock would do.
> >
> > What about this variant:
> >
> >   1. Keep the old CaR code in place.
> >
> >   2. Make CaR driver to scan whole device-tree for the legacy PMC clocks.
> >
> >   3. If legacy clock is found, then register PMC clocks from CaR.
> >
> >   4. If legacy clocks are not found, then don't register PMC clocks from
> > CaR.
> >
> >   5. Add clocks support to the PMC driver and only register them if
> > legacy clocks are not registered by CaR.
> >
> > Now both old and new DTBs can co-exist and work, everyone happy.
> 
> That seems even more work.. Today the only upstream user is audio.
> Currently these clocks are setup by the CAR clock driver. However
> as they will move to the PMC driver, this mechanism cannot be used.
> Hence the plan is to modify the audio driver to check for the PMC clocks
> in DT and if they are not available use the CAR clocks as fallback.
> The whole reason the clocks move to the PMC driver, is that when PMC
> becomes secure, all accesses have to go via an SMC. Given that we don't
> want SMCs all over the Tegra drivers, it's a good opportunity to move
> the PMC clock handling into the PMC driver. PMC can be secure with both
> 'new' and old DTs, so just registering the PMC clocks in the CAR driver
> if legacy clocks are found in the DT, won't always work.
> 

Given the audio driver needs to change anyway, we can indeed use 1 clock
per PMC clk_out_ rather than 2 as we have today. As this models the hw
slightly better, I think we should do that as you suggested.

Peter.