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

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Message-ID: <db3bee1e-1bfa-2f9e-9ed1-91b98554556a@gmail.com>
Date:   Tue, 10 Dec 2019 20:41:39 +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

09.12.2019 23:46, Sowjanya Komatineni пишет:
> 
> On 12/9/19 12:12 PM, Dmitry Osipenko wrote:
>> 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?
> 
> PMC CLK1/2/3 possible sources are OSC_DIV1, OSC_DIV2, OSC_DIV4,
> EXTPERIPH from CAR.
> 
> OSC_DIV1/2/4 are with internal dividers at the OSC Pads
> 
> EXTPERIPH is from CAR and it has reset and enable controls along with
> clock source selections to choose one of the PLLA_OUT0, CLK_S,
> PLLP_OUT0, CLK_M, PLLE_OUT0

Are you sure that EXTPERIPH has a reset? What will it reset? Why it's
not documented in TRM?

> So, PMC CLK1/2/4 possible parents are OSC_DIV1, OSC_DIV2, OSC_DIV4, EXTERN.
> 
> 
> CLK1/2/3 also has Pinmux to route EXTPERIPH output on to these pins.

Could you please clarify what are "these" pins? Perhaps you meant the
EXTERN pin of PMC?

> When EXTERN output clock is selected for these PMC clocks thru
> CLKx_SRC_SEL, output clock is from driver by EXTPERIPH from CAR via
> Pinmux logic or driven as per CLKx_SRC_SEL bypassing pinmux based on
> CLKx_ACCEPT_REQ bit.
> 
> 
> PMC Clock control register has bit CLKx_ACCEPT_REQ
> When CLKx_ACCEPT_REQ = 0, output clock driver is from by EXTPERIPH
> through the pinmux
> When CLKx_ACCEPT_REQ = 1, output clock is based on CLKx_SRC_SEL bits
> (OSC_DIV1/2/4 and EXTPERIPH clock bypassing the pinmux)
> 
> FORCE_EN bit in PMC CLock control register forces the clock to run
> regardless of this.

Okay.