linux-kernel - Re: [PATCH V6 09/21] clk: tegra: clk-super: Fix to enable PLLP branches to CPU

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Message-ID: <07897688-2a02-b7a7-7048-72c4078d26a2@gmail.com>
Date:   Mon, 22 Jul 2019 10:17:21 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com, tglx@...utronix.de,
        jason@...edaemon.net, marc.zyngier@....com,
        linus.walleij@...aro.org, stefan@...er.ch, mark.rutland@....com
Cc:     pdeschrijver@...dia.com, pgaikwad@...dia.com, sboyd@...nel.org,
        linux-clk@...r.kernel.org, linux-gpio@...r.kernel.org,
        jckuo@...dia.com, josephl@...dia.com, talho@...dia.com,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        mperttunen@...dia.com, spatra@...dia.com, robh+dt@...nel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH V6 09/21] clk: tegra: clk-super: Fix to enable PLLP
 branches to CPU

22.07.2019 10:12, Sowjanya Komatineni пишет:
> 
> On 7/21/19 11:32 PM, Dmitry Osipenko wrote:
>> 22.07.2019 6:17, Sowjanya Komatineni пишет:
>>> On 7/21/19 3:39 PM, Sowjanya Komatineni wrote:
>>>> On 7/21/19 2:16 PM, Dmitry Osipenko wrote:
>>>>> 21.07.2019 22:40, Sowjanya Komatineni пишет:
>>>>>> This patch has a fix to enable PLLP branches to CPU before changing
>>>>>> the CPU clusters clock source to PLLP for Gen5 Super clock.
>>>>>>
>>>>>> During system suspend entry and exit, CPU source will be switched
>>>>>> to PLLP and this needs PLLP branches to be enabled to CPU prior to
>>>>>> the switch.
>>>>>>
>>>>>> On system resume, warmboot code enables PLLP branches to CPU and
>>>>>> powers up the CPU with PLLP clock source.
>>>>>>
>>>>>> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
>>>>>> ---
>>>>>>    drivers/clk/tegra/clk-super.c            | 11 +++++++++++
>>>>>>    drivers/clk/tegra/clk-tegra-super-gen4.c |  4 ++--
>>>>>>    drivers/clk/tegra/clk.h                  |  4 ++++
>>>>>>    3 files changed, 17 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/clk/tegra/clk-super.c
>>>>>> b/drivers/clk/tegra/clk-super.c
>>>>>> index 39ef31b46df5..d73c587e4853 100644
>>>>>> --- a/drivers/clk/tegra/clk-super.c
>>>>>> +++ b/drivers/clk/tegra/clk-super.c
>>>>>> @@ -28,6 +28,9 @@
>>>>>>    #define super_state_to_src_shift(m, s) ((m->width * s))
>>>>>>    #define super_state_to_src_mask(m) (((1 << m->width) - 1))
>>>>>>    +#define CCLK_SRC_PLLP_OUT0 4
>>>>>> +#define CCLK_SRC_PLLP_OUT4 5
>>>>>> +
>>>>>>    static u8 clk_super_get_parent(struct clk_hw *hw)
>>>>>>    {
>>>>>>        struct tegra_clk_super_mux *mux = to_clk_super_mux(hw);
>>>>>> @@ -97,6 +100,14 @@ static int clk_super_set_parent(struct clk_hw
>>>>>> *hw, u8 index)
>>>>>>            if (index == mux->div2_index)
>>>>>>                index = mux->pllx_index;
>>>>>>        }
>>>>>> +
>>>>>> +    /*
>>>>>> +     * Enable PLLP branches to CPU before selecting PLLP source
>>>>>> +     */
>>>>>> +    if ((mux->flags & TEGRA_CPU_CLK) &&
>>>>>> +        ((index == CCLK_SRC_PLLP_OUT0) || (index ==
>>>>>> CCLK_SRC_PLLP_OUT4)))
>>>>>> +        tegra_clk_set_pllp_out_cpu(true);
>>>>> Should somewhere here be tegra_clk_set_pllp_out_cpu(false) when
>>>>> switching from PLLP?
>>>> PLLP may be used for other CPU clusters.
>>> Though to avoid flag and check needed to make sure other CPU is not
>>> using before disabling PLLP branch to CPU.
>>>
>>> But leaving it enabled shouldn't impact much as clock source mux is
>>> after this in design anyway.
>>>
>>> But can add as well if its clear that way.
>> The TRM doc says "The CPU subsystem supports a switch-cluster mode
>> meaning that only one of the clusters can be active at any given time".
>>
>> Given that cluster-switching isn't supported in upstream, I don't think
>> that you need to care about the other cluster at all, at least for now.
>>
>> The cluster-switching implementation in upstream is very complicated
>> because it requires a special "hotplugging" CPU governor, which
>> apparently no other platform needs.
>>
>> [snip]
> 
> This patch enables PLLP branches to CPU for both CPUG & CPULP if they
> use PLLP source.
> 
> So, to disable PLLP out CPU when not in use, we still need check for
> other cluster because during resume both LP CPU and G CPU gets restored.
> CPUG runs from PLLP on resume and when it does super clk restore for LP
> CPU which may not be using PLLP, but as both uses same super mux
> clk_ops, without check (for PLLP branch to CPU in use) disabling PLLP
> branch to CPU during LP CPU restore looses clock to CPU G as well which
> is running from PLLP.
> 
> Will add check and disable PLLP if not in use in next version... this
> need extern flag as well to mark PLLP usage with either of CPU's.

I still don't understand why do you need to care about LP cluster at
all, given that it's always in a power-gated state.