linux-kernel - Re: [PATCH v8 11/21] clk: tegra: clk-dfll: Add suspend and resume support

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Message-ID: <84a0d46a-bca2-1000-a2a6-8890ee702dd3@gmail.com>
Date:   Fri, 9 Aug 2019 21:00:16 +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, rjw@...ysocki.net,
        viresh.kumar@...aro.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v8 11/21] clk: tegra: clk-dfll: Add suspend and resume
 support

09.08.2019 19:39, Sowjanya Komatineni пишет:
> 
> On 8/9/19 5:23 AM, Dmitry Osipenko wrote:
>> 09.08.2019 2:46, Sowjanya Komatineni пишет:
>>> This patch implements DFLL suspend and resume operation.
>>>
>>> During system suspend entry, CPU clock will switch CPU to safe
>>> clock source of PLLP and disables DFLL clock output.
>>>
>>> DFLL driver suspend confirms DFLL disable state and errors out on
>>> being active.
>>>
>>> DFLL is re-initialized during the DFLL driver resume as it goes
>>> through complete reset during suspend entry.
>>>
>>> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
>>> ---
>>>   drivers/clk/tegra/clk-dfll.c               | 56 ++++++++++++++++++++++++++++++
>>>   drivers/clk/tegra/clk-dfll.h               |  2 ++
>>>   drivers/clk/tegra/clk-tegra124-dfll-fcpu.c |  1 +
>>>   3 files changed, 59 insertions(+)
>>>
>>> diff --git a/drivers/clk/tegra/clk-dfll.c b/drivers/clk/tegra/clk-dfll.c
>>> index f8688c2ddf1a..eb298a5d7be9 100644
>>> --- a/drivers/clk/tegra/clk-dfll.c
>>> +++ b/drivers/clk/tegra/clk-dfll.c
>>> @@ -1487,6 +1487,7 @@ static int dfll_init(struct tegra_dfll *td)
>>>       td->last_unrounded_rate = 0;
>>>         pm_runtime_enable(td->dev);
>>> +    pm_runtime_irq_safe(td->dev);
>>>       pm_runtime_get_sync(td->dev);
>>>         dfll_set_mode(td, DFLL_DISABLED);
>>> @@ -1513,6 +1514,61 @@ static int dfll_init(struct tegra_dfll *td)
>>>       return ret;
>>>   }
>>>   +/**
>>> + * tegra_dfll_suspend - check DFLL is disabled
>>> + * @dev: DFLL device *
>>> + *
>>> + * DFLL clock should be disabled by the CPUFreq driver. So, make
>>> + * sure it is disabled and disable all clocks needed by the DFLL.
>>> + */
>>> +int tegra_dfll_suspend(struct device *dev)
>>> +{
>>> +    struct tegra_dfll *td = dev_get_drvdata(dev);
>>> +
>>> +    if (dfll_is_running(td)) {
>>> +        dev_err(td->dev, "dfll is enabled while shouldn't be\n");
>>> +        return -EBUSY;
>>> +    }
>>> +
>>> +    reset_control_assert(td->dvco_rst);
>>> +
>>> +    return 0;
>>> +}
>>> +EXPORT_SYMBOL(tegra_dfll_suspend);
>>> +
>>> +/**
>>> + * tegra_dfll_resume - reinitialize DFLL on resume
>>> + * @dev: DFLL instance
>>> + *
>>> + * DFLL is disabled and reset during suspend and resume.
>>> + * So, reinitialize the DFLL IP block back for use.
>>> + * DFLL clock is enabled later in closed loop mode by CPUFreq
>>> + * driver before switching its clock source to DFLL output.
>>> + */
>>> +int tegra_dfll_resume(struct device *dev)
>>> +{
>>> +    struct tegra_dfll *td = dev_get_drvdata(dev);
>>> +
>>> +    reset_control_deassert(td->dvco_rst);
>> This doesn't look right because I assume that DFLL resetting is
>> synchronous and thus clk should be enabled in order for reset to
>> propagate inside hardware.
>>
>>> +    pm_runtime_get_sync(td->dev);
>> Hence it will be better to remove the above reset_control_deassert() and
>> add here:
>>
>>     reset_control_reset(td->dvco_rst);
> 
> By the time dfll resume happens, dfll controller clock will already be enabled.
> 
> so doing reset de-assert before pm_runtime seems ok.

I don't see what enables the DFLL clock because it should be enabled by the CPUFreq driver
on resume from suspend and resume happens after resuming of the DFLL driver.