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 12:46:47 -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 12/9/19 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

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.


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.