linux-kernel - Re: [PATCH v7 01/20] pinctrl: tegra: Add suspend and resume support

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Date:   Tue, 6 Aug 2019 14:54:18 -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>, <rjw@...ysocki.net>,
        <viresh.kumar@...aro.org>, <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v7 01/20] pinctrl: tegra: Add suspend and resume support


On 8/6/19 10:59 AM, Dmitry Osipenko wrote:
> 05.08.2019 21:06, Sowjanya Komatineni пишет:
>> On 8/5/19 3:50 AM, Dmitry Osipenko wrote:
>>> 01.08.2019 0:10, Sowjanya Komatineni пишет:
>>>> This patch adds support for Tegra pinctrl driver suspend and resume.
>>>>
>>>> During suspend, context of all pinctrl registers are stored and
>>>> on resume they are all restored to have all the pinmux and pad
>>>> configuration for normal operation.
>>>>
>>>> Acked-by: Thierry Reding <treding@...dia.com>
>>>> Reviewed-by: Dmitry Osipenko <digetx@...il.com>
>>>> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
>>>> ---
>>>>    drivers/pinctrl/tegra/pinctrl-tegra.c | 59
>>>> +++++++++++++++++++++++++++++++++++
>>>>    drivers/pinctrl/tegra/pinctrl-tegra.h |  3 ++
>>>>    2 files changed, 62 insertions(+)
>>>>
>>>> diff --git a/drivers/pinctrl/tegra/pinctrl-tegra.c
>>>> b/drivers/pinctrl/tegra/pinctrl-tegra.c
>>>> index 186ef98e7b2b..e3a237534281 100644
>>>> --- a/drivers/pinctrl/tegra/pinctrl-tegra.c
>>>> +++ b/drivers/pinctrl/tegra/pinctrl-tegra.c
>>>> @@ -631,6 +631,58 @@ static void
>>>> tegra_pinctrl_clear_parked_bits(struct tegra_pmx *pmx)
>>>>        }
>>>>    }
>>>>    +static size_t tegra_pinctrl_get_bank_size(struct device *dev,
>>>> +                      unsigned int bank_id)
>>>> +{
>>>> +    struct platform_device *pdev = to_platform_device(dev);
>>>> +    struct resource *res;
>>>> +
>>>> +    res = platform_get_resource(pdev, IORESOURCE_MEM, bank_id);
>>>> +
>>>> +    return resource_size(res) / 4;
>>>> +}
>>>> +
>>>> +static int tegra_pinctrl_suspend(struct device *dev)
>>>> +{
>>>> +    struct tegra_pmx *pmx = dev_get_drvdata(dev);
>>>> +    u32 *backup_regs = pmx->backup_regs;
>>>> +    u32 *regs;
>>>> +    size_t bank_size;
>>>> +    unsigned int i, k;
>>>> +
>>>> +    for (i = 0; i < pmx->nbanks; i++) {
>>>> +        bank_size = tegra_pinctrl_get_bank_size(dev, i);
>>>> +        regs = pmx->regs[i];
>>>> +        for (k = 0; k < bank_size; k++)
>>>> +            *backup_regs++ = readl_relaxed(regs++);
>>>> +    }
>>>> +
>>>> +    return pinctrl_force_sleep(pmx->pctl);
>>>> +}
>>>> +
>>>> +static int tegra_pinctrl_resume(struct device *dev)
>>>> +{
>>>> +    struct tegra_pmx *pmx = dev_get_drvdata(dev);
>>>> +    u32 *backup_regs = pmx->backup_regs;
>>>> +    u32 *regs;
>>>> +    size_t bank_size;
>>>> +    unsigned int i, k;
>>>> +
>>>> +    for (i = 0; i < pmx->nbanks; i++) {
>>>> +        bank_size = tegra_pinctrl_get_bank_size(dev, i);
>>>> +        regs = pmx->regs[i];
>>>> +        for (k = 0; k < bank_size; k++)
>>>> +            writel_relaxed(*backup_regs++, regs++);
>>>> +    }
>>> I'm now curious whether any kind of barrier is needed after the
>>> writings. The pmx_writel() doesn't insert a barrier after the write and
>>> seems it just misuses writel, which actually should be writel_relaxed()
>>> + barrier, IIUC.
>> pmx_writel uses writel and it has wmb before raw_write which complete
>> all writes initiated prior to this.
>>
>> By misusing writel, you mean to have barrier after register write?
> Yes, at least to me it doesn't make much sense for this driver to stall
> before the write. It's the pinctrl user which should be taking care
> about everything to be ready before making a change to the pinctrl's
> configuration.
>
>>> It's also not obvious whether PINCTRL HW has any kind of write-FIFO and
>>> thus maybe read-back + rmb() is needed in order ensure that writes are
>>> actually completed.
>> I believe adding write barrier wmb after writel_relaxed should be good
>> rather than doing readback + rmb
>>> The last thing which is not obvious is when the new configuration
>>> actually takes into effect, does it happen immediately or maybe some
>>> delay is needed?
>>>
>>> [snip]
>> Based on internal design there is no internal delay and it all depends
>> on APB rate that it takes to write to register.
>>
>> Pinmux value change to reflect internally might take couple of clock
>> cycles which is much faster than SW can read.
> Still not quite obvious if it's possible to have a case where some
> hardware is touched before necessary pinctrl change is fully completed
> and then to get into trouble because of it.

To be safer, will add write barrier after all writes in resume and also 
will have separate patch for pmx_writel fix to use writel_relaxed 
followed by write barrier.

Thanks

Sowjanya