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

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Message-ID: <fc6403e6-0022-f505-8864-70bc047207c9@gmail.com>
Date:   Mon, 22 Jul 2019 10:30:01 +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 10:24, Sowjanya Komatineni пишет:
> 
> On 7/22/19 12:17 AM, Dmitry Osipenko wrote:
>> 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.
> 
> cclk_lp is registered thru super clk mux which uses same clk_ops as cclk_g.
> 
> during restore, cclk_lp also gets restored. So both cclk_lp & cclk_g
> goes thru same clk_ops
> 
> In this patch, I marked super flags with TEGRA_CPU_CLK for both cclk_lp
> & cclk_g.
> 
> So when cclk_lp restore happens, it goes thru same set_parent clk_ops
> and as its source is not PLLP, it tries to disable PLLP_OUT_CPU if its
> disabled without adding check for PLLP being in use by other cluster.

Ah, okay.

> So either I should not mark cclk_lp as TEGRA_CPU_CLK and mark cclk_g
> only as TEGRA_CPU_CLK so PLLP out to CPU can be disabled without check
> if its not the source.
> 
> OR
> 
> With TEGRA_CPU_CLK used for both cclk_lp & cclk_g, need to add check if
> PLLP is in use so during cclk_lp restore it doesnt disable PLLP out to CPU.
> 
> 
> To simplify without check, will just mark cclk_g super clock flag only
> as TEGRA_CPU_CLK so PLLP_OUT_CPU enable or disable happens only for CPUG

Sounds good. Then please add a brief comment to the CPULP, telling why
it misses the flag, for the record.