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 13:36:39 -0800
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.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


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.
>