linux-kernel - Re: [PATCH v7 06/20] clk: tegra: Support for OSC context save and restore

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Date:   Thu, 1 Aug 2019 21:42:39 +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 v7 06/20] clk: tegra: Support for OSC context save and
 restore

01.08.2019 21:06, Sowjanya Komatineni пишет:
> 
> On 8/1/19 3:53 AM, Dmitry Osipenko wrote:
>> 01.08.2019 0:04, Sowjanya Komatineni пишет:
>>> On 7/31/19 4:11 AM, Dmitry Osipenko wrote:
>>>> 31.07.2019 3:20, Sowjanya Komatineni пишет:
>>>>> This patch adds support for saving OSC clock frequency and the
>>>>> drive-strength during OSC clock init and creates an API to restore
>>>>> OSC control register value from the saved context.
>>>>>
>>>>> This API is invoked by Tegra210 clock driver during system resume
>>>>> to restore the  OSC clock settings.
>>>>>
>>>>> Acked-by: Thierry Reding <treding@...dia.com>
>>>>> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
>>>>> ---
>>>>>    drivers/clk/tegra/clk-tegra-fixed.c | 15 +++++++++++++++
>>>>>    drivers/clk/tegra/clk.h             |  1 +
>>>>>    2 files changed, 16 insertions(+)
>>>>>
>>>>> diff --git a/drivers/clk/tegra/clk-tegra-fixed.c
>>>>> b/drivers/clk/tegra/clk-tegra-fixed.c
>>>>> index 8d91b2b191cf..7c6c8abfcde6 100644
>>>>> --- a/drivers/clk/tegra/clk-tegra-fixed.c
>>>>> +++ b/drivers/clk/tegra/clk-tegra-fixed.c
>>>>> @@ -17,6 +17,10 @@
>>>>>    #define OSC_CTRL            0x50
>>>>>    #define OSC_CTRL_OSC_FREQ_SHIFT        28
>>>>>    #define OSC_CTRL_PLL_REF_DIV_SHIFT    26
>>>>> +#define OSC_CTRL_MASK            (0x3f2 |    \
>>>>> +                    (0xf << OSC_CTRL_OSC_FREQ_SHIFT))
>>>>> +
>>>>> +static u32 osc_ctrl_ctx;
>>>>>      int __init tegra_osc_clk_init(void __iomem *clk_base, struct
>>>>> tegra_clk *clks,
>>>>>                      unsigned long *input_freqs, unsigned int num,
>>>>> @@ -29,6 +33,7 @@ int __init tegra_osc_clk_init(void __iomem
>>>>> *clk_base, struct tegra_clk *clks,
>>>>>        unsigned osc_idx;
>>>>>          val = readl_relaxed(clk_base + OSC_CTRL);
>>>>> +    osc_ctrl_ctx = val & OSC_CTRL_MASK;
>>>>>        osc_idx = val >> OSC_CTRL_OSC_FREQ_SHIFT;
>>>>>          if (osc_idx < num)
>>>>> @@ -96,3 +101,13 @@ void __init tegra_fixed_clk_init(struct tegra_clk
>>>>> *tegra_clks)
>>>>>            *dt_clk = clk;
>>>>>        }
>>>>>    }
>>>>> +
>>>>> +void tegra_clk_osc_resume(void __iomem *clk_base)
>>>>> +{
>>>>> +    u32 val;
>>>>> +
>>>>> +    val = readl_relaxed(clk_base + OSC_CTRL) & ~OSC_CTRL_MASK;
>>>>> +    val |= osc_ctrl_ctx;
>>>>> +    writel_relaxed(val, clk_base + OSC_CTRL);
>>>> Why a full raw u32 OSC_CTRL value couldn't be simply saved and
>>>> restored?
>>> Storing and restoring only required fields to avoid accidental
>>> misconfiguration.
>>>
>>> OSC_CTRL register has other bits (PLL_REF_DIV) which are configured by
>>> BR depending on OSC_FREQ and also setting PLL_REF_DIV while PLLS are in
>>> use is not safe.
>> I'm looking at the clk-driver sources and see that none of the Tegra
>> drivers ever change the OSC_CTRL configuration, T30/114 even have
>> #defines for the OSC_CTRL that are unused.
>>
>> So, this leads to a question.. does any bootloader really ever change
>> the OSC_CTRL such that it differs after resume from suspend in
>> comparison to the value at the time of kernel's booting up?
> 
> For Tegra210, bootloader programs OSC_CTRL register for drivestrength
> programming.
> 
> These settings need to be restored to the same on SC7 exit as they gets
> reset during SC7 entry.

Okay, thank you for the clarification.