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

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Message-ID: <b386ff76-b72d-948b-b41d-7ed9ce3a4400@nvidia.com>
Date:   Mon, 22 Jul 2019 00:36:27 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.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


On 7/22/19 12:30 AM, Dmitry Osipenko wrote:
> 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.

Sure, will add comment.