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

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Date:   Mon, 16 Dec 2019 18:49:21 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Peter De Schrijver <pdeschrijver@...dia.com>
Cc:     Sowjanya Komatineni <skomatineni@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com,
        mperttunen@...dia.com, sboyd@...nel.org,
        gregkh@...uxfoundation.org, tglx@...utronix.de, robh+dt@...nel.org,
        mark.rutland@....com, allison@...utok.net, 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,
        broonie@...nel.org, perex@...ex.cz, tiwai@...e.com,
        alexios.zavras@...el.com, alsa-devel@...a-project.org
Subject: Re: [PATCH v3 03/15] soc: tegra: Add Tegra PMC clock registrations
 into PMC driver

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.