linux-kernel - Re: [PATCH v7 07/20] clk: tegra: clk-periph: Add save and restore support

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Date:   Fri, 2 Aug 2019 13:37:50 -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 v7 07/20] clk: tegra: clk-periph: Add save and restore
 support


On 8/2/19 1:20 PM, Dmitry Osipenko wrote:
> 02.08.2019 21:43, Sowjanya Komatineni пишет:
>> On 8/2/19 5:32 AM, Dmitry Osipenko wrote:
>>> 31.07.2019 3:20, Sowjanya Komatineni пишет:
>>>> This patch implements save and restore context for peripheral fixed
>>>> clock ops, peripheral gate clock ops, sdmmc mux clock ops, and
>>>> peripheral clock ops.
>>>>
>>>> During system suspend, core power goes off and looses the settings
>>>> of the Tegra CAR controller registers.
>>>>
>>>> So during suspend entry clock and reset state of peripherals is saved
>>>> and on resume they are restored to have clocks back to same rate and
>>>> state as before suspend.
>>>>
>>>> Acked-by: Thierry Reding <treding@...dia.com>
>>>> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
>>>> ---
>>>>    drivers/clk/tegra/clk-periph-fixed.c | 33
>>>> ++++++++++++++++++++++++++++++++
>>>>    drivers/clk/tegra/clk-periph-gate.c  | 34
>>>> +++++++++++++++++++++++++++++++++
>>>>    drivers/clk/tegra/clk-periph.c       | 37
>>>> ++++++++++++++++++++++++++++++++++++
>>>>    drivers/clk/tegra/clk-sdmmc-mux.c    | 28 +++++++++++++++++++++++++++
>>>>    drivers/clk/tegra/clk.h              |  6 ++++++
>>>>    5 files changed, 138 insertions(+)
>>>>
>>>> diff --git a/drivers/clk/tegra/clk-periph-fixed.c
>>>> b/drivers/clk/tegra/clk-periph-fixed.c
>>>> index c088e7a280df..21b24530fa00 100644
>>>> --- a/drivers/clk/tegra/clk-periph-fixed.c
>>>> +++ b/drivers/clk/tegra/clk-periph-fixed.c
>>>> @@ -60,11 +60,44 @@ tegra_clk_periph_fixed_recalc_rate(struct clk_hw
>>>> *hw,
>>>>        return (unsigned long)rate;
>>>>    }
>>>>    +static int tegra_clk_periph_fixed_save_context(struct clk_hw *hw)
>>>> +{
>>>> +    struct tegra_clk_periph_fixed *fixed =
>>>> to_tegra_clk_periph_fixed(hw);
>>>> +    u32 mask = 1 << (fixed->num % 32);
>>> This could be BIT(fixed->num % 32).
>>>
>>>> +    fixed->enb_ctx = readl_relaxed(fixed->base +
>>>> fixed->regs->enb_reg) &
>>>> +             mask;
>>>> +    fixed->rst_ctx = readl_relaxed(fixed->base +
>>>> fixed->regs->rst_reg) &
>>>> +             mask;
>>> The enb_ctx/rst_ctx are booleans, while you assigning an integer value
>>> here. You're getting away here because bool is an 32bit unsigned int,
>>> but you shouldn't rely on it and always explicitly convert to a bool.
>>>
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +static void tegra_clk_periph_fixed_restore_context(struct clk_hw *hw)
>>>> +{
>>>> +    struct tegra_clk_periph_fixed *fixed =
>>>> to_tegra_clk_periph_fixed(hw);
>>>> +    u32 mask = 1 << (fixed->num % 32);
>>>> +
>>>> +    if (fixed->enb_ctx)
>>>> +        writel_relaxed(mask, fixed->base + fixed->regs->enb_set_reg);
>>>> +    else
>>>> +        writel_relaxed(mask, fixed->base + fixed->regs->enb_clr_reg);
>>>> +
>>>> +    udelay(2);
>>> Will be better to read out and compare the hardware's state with the
>>> restored one, then bail out if the state is unchanged.
>>>
>>> Shouldn't it be fence_udelay()?
>>>
>>>> +    if (!fixed->rst_ctx) {
>>>> +        udelay(5); /* reset propogation delay */
>>> Why delaying is done before the writing to the reset register?
>> During SC7 exit, peripheral reset state is set to POR state. So some
>> peripherals will already be in reset state and making sure of
>> propagation delay before releasing from reset.
>>
>> It should be rst_clr_reg. will fix in next rev
>>
>>>> +        writel_relaxed(mask, fixed->base + fixed->regs->rst_reg);
>>> I'm not quite sure what's going on here, this looks wrong.
>>>
>>> 1. rst_reg points to RST_DEVICES_x
>>> 2. Each bit of RST_DEVICES_x represents the reset-assertion state of
>>> each individual device
>>> 3. By writing to rst_reg, all (!) devices are deasserted, except the one
>>> device which corresponds to the mask
>>> 4. The reset is asserted for a single device, while !fixed->rst_ctx
>>> means that it actually should be deasserted (?)
>>>
>>> Apparently you should use rst_set_reg / rst_clr_reg.
>> Yes, It should be rst_clr_reg. will fix in next rev
>>>> +    }
>>> What about the case where rst_ctx=true?
>> ON SC7 exit, state of RST_DEV will be POR state where most peripherals
>> will already be in reset state.
>>
>> Few of them which are not in reset state in POR values are those that
>> need to stay de-asserted across the boot states anyway.
> Okay, sounds reasonable.
>
> BTW, it would be nice if you could add a brief clarifying comment to the
> code for each of the questions asked during of the review.
OK, Will add comments in code ...