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

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Message-ID: <f6ac50af-c3a5-1fef-2e0d-a9ecadeb2495@gmail.com>
Date:   Mon, 22 Jul 2019 09:32:44 +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 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]