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

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Message-ID: <d9bbe208-6cd3-6a28-3e43-fdd566699b1d@nvidia.com>
Date:   Mon, 22 Jul 2019 00:12:49 -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 7/21/19 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.