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

From: Dmitry Osipenko <digetx@gmail.com>
To: Peter De Schrijver <pdeschrijver@nvidia.com>
Cc: mark.rutland@arm.com, alsa-devel@alsa-project.org,
	pgaikwad@nvidia.com, lgirdwood@gmail.com,
	mturquette@baylibre.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,
	spujar@nvidia.com, devicetree@vger.kernel.org, arnd@arndb.de,
	markz@nvidia.com, alexios.zavras@intel.com, robh+dt@kernel.org,
	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, linux-kernel@vger.kernel.org,
	vidyas@nvidia.com, Jisheng.Zhang@synaptics.com,
	broonie@kernel.org, Sowjanya Komatineni <skomatineni@nvidia.com>
Subject: Re: [alsa-devel] [PATCH v3 03/15] soc: tegra: Add Tegra PMC clock registrations into PMC driver
Date: Mon, 16 Dec 2019 18:49:21 +0300	[thread overview]
Message-ID: <fa538845-cb8e-cf88-34be-3ceb2daa63c2@gmail.com> (raw)
In-Reply-To: <20191216152435.GD28289@pdeschrijver-desktop.Nvidia.com>

16.12.2019 18:24, Peter De Schrijver пишет:
> 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.
> 

Okay, let's try and see how it will go.
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