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

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Message-ID: <3f1c9325-3017-62be-1e3b-82fd28540fdf@nvidia.com>
Date:   Tue, 10 Dec 2019 08:53:42 -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 3:03 PM, Sowjanya Komatineni wrote:
>
> On 12/9/19 12:46 PM, Sowjanya Komatineni wrote:
>>
>> 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.
>>>>>
> Reg clk_m_div2/3, they are dividers at OSC pad and not really internal 
> to PMC block.
>
> current clock driver creates clk_m_div clocks which should actually be 
> osc_div2/osc_div4 clocks with osc as parent.
>
> There are no clk_m_div2 and clk_m_div4 from clk_m
>
> Will fix this 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.

PMC clock gate is based on the state of CLKx_ACCEPT_REQ and FORCE_EN 
like explained above.

CLKx_ACCEPT_REQ is 0 default and FORCE_EN acts as gate to enable/disable 
EXTPERIPH clock output to PMC CLK_OUT_1/2/3.

So I believe we need to register as MUX and Gate rather than as a single 
clock. Please confirm.