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

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Date:   Mon, 9 Dec 2019 23:12:35 +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

08.12.2019 00:36, Sowjanya Komatineni пишет:
> 
> On 12/7/19 11:59 AM, Sowjanya Komatineni wrote:
>>
>> On 12/7/19 8:00 AM, Dmitry Osipenko wrote:
>>> 07.12.2019 18:53, Dmitry Osipenko пишет:
>>>> 07.12.2019 18:47, Dmitry Osipenko пишет:
>>>>> 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?
> 
> Was following existing clk-tegra-pmc as I am not sure of reason for
> having these clocks registered as separate mux and gate clocks.
> 
> Yes, PMC clocks can be registered as single clock and can use clk_ops
> for set/get parent and enable/disable.
> 
> enable/disable of PMC clocks is for force-enable to force the clock to
> run regardless of ACCEPT_REQ or INVERT_REQ.
> 
>>>> 4. clk_m_div2/4 are internal PMC OSC dividers and thus these clocks
>>>> should belong to PMC.
>>> Also, it should be "osc" and not "clk_m".
>>
>> I followed the same parents as it were in existing clk-tegra-pmc driver.
>>
>> Yeah they are wrong and they should be from osc and not clk_m.
>>
>> Will fix in next version.
>>

Could you please describe the full EXTPERIPH clock topology and how the
pinmux configuration is related to it all?

What is internal to the Tegra chip and what are the external outputs?

Is it possible to bypass PMC on T30+ for the EXTPERIPH clocks?