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

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Date:   Sat, 7 Dec 2019 18:47:48 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com,
        mperttunen@...dia.com, gregkh@...uxfoundation.org,
        sboyd@...nel.org, tglx@...utronix.de, robh+dt@...nel.org,
        mark.rutland@....com
Cc:     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,
        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

07.12.2019 17:28, Dmitry Osipenko пишет:
> 06.12.2019 05:48, Sowjanya Komatineni пишет:
>> Tegra210 and prior Tegra PMC has clk_out_1, clk_out_2, clk_out_3 with
>> mux and gate for each of these clocks.
>>
>> Currently these PMC clocks are registered by Tegra clock driver using
>> clk_register_mux and clk_register_gate by passing PMC base address
>> and register offsets and PMC programming for these clocks happens
>> through direct PMC access by the clock driver.
>>
>> With this, when PMC is in secure mode any direct PMC access from the
>> non-secure world does not go through and these clocks will not be
>> functional.
>>
>> This patch adds these clocks registration with PMC as a clock provider
>> for these clocks. clk_ops callback implementations for these clocks
>> uses tegra_pmc_readl and tegra_pmc_writel which supports PMC programming
>> in secure mode and non-secure mode.
>>
>> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
>> ---

[snip]

>> +
>> +static const struct clk_ops pmc_clk_gate_ops = {
>> +	.is_enabled = pmc_clk_is_enabled,
>> +	.enable = pmc_clk_enable,
>> +	.disable = pmc_clk_disable,
>> +};
> 
> What's the benefit of separating GATE from the MUX?
> 
> I think it could be a single clock.

According to TRM:

1. GATE and MUX are separate entities.

2. GATE is the parent of MUX (see PMC's CLK_OUT paths diagram in TRM).

3. PMC doesn't gate EXTPERIPH clock but could "force-enable" it, correct?

[snip]