linux-kernel - Re: [PATCH v1] soc/tegra: pmc: Query PCLK clock rate at probe time

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Message-ID: <aa12115c-bf1c-f50b-f38a-97fb398d1af0@nvidia.com>
Date:   Thu, 18 Jul 2019 10:53:01 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>
CC:     <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] soc/tegra: pmc: Query PCLK clock rate at probe time


On 18/07/2019 10:45, Jon Hunter wrote:
> 
> On 08/07/2019 00:08, Dmitry Osipenko wrote:
>> The PCLK clock is running off SCLK, which is a critical clock that is
>> very unlikely to randomly change its rate. It's also a bit clumsy (and
>> apparently incorrect) to query the clock's rate with interrupts being
>> disabled because clk_get_rate() takes a mutex and that's the case during
>> suspend/cpuidle entering. Lastly, it's better to always fully reprogram
>> PMC state because it's not obvious whether it could be changed after SC7.
> 
> I agree with the first part, but I would drop the last sentence because
> I see no evidence of this. Maybe Peter can confirm.
> 
>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>> ---
>>  drivers/soc/tegra/pmc.c | 26 +++++++++++---------------
>>  1 file changed, 11 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/soc/tegra/pmc.c b/drivers/soc/tegra/pmc.c
>> index 9f9c1c677cf4..532e0ada012b 100644
>> --- a/drivers/soc/tegra/pmc.c
>> +++ b/drivers/soc/tegra/pmc.c
>> @@ -1433,6 +1433,7 @@ void tegra_pmc_set_suspend_mode(enum tegra_suspend_mode mode)
>>  void tegra_pmc_enter_suspend_mode(enum tegra_suspend_mode mode)
>>  {
>>  	unsigned long long rate = 0;
>> +	u64 ticks;
>>  	u32 value;
>>  
>>  	switch (mode) {
>> @@ -1441,7 +1442,7 @@ void tegra_pmc_enter_suspend_mode(enum tegra_suspend_mode mode)
>>  		break;
>>  
>>  	case TEGRA_SUSPEND_LP2:
>> -		rate = clk_get_rate(pmc->clk);
>> +		rate = pmc->rate;
> 
> There is another call to clk_get_rate() that could be removed as well.
> 
>>  		break;
>>  
>>  	default:
>> @@ -1451,26 +1452,20 @@ void tegra_pmc_enter_suspend_mode(enum tegra_suspend_mode mode)
>>  	if (WARN_ON_ONCE(rate == 0))
>>  		rate = 100000000;
>>  
>> -	if (rate != pmc->rate) {
>> -		u64 ticks;
>> -
>> -		ticks = pmc->cpu_good_time * rate + USEC_PER_SEC - 1;
>> -		do_div(ticks, USEC_PER_SEC);
>> -		tegra_pmc_writel(pmc, ticks, PMC_CPUPWRGOOD_TIMER);
>> -
>> -		ticks = pmc->cpu_off_time * rate + USEC_PER_SEC - 1;
>> -		do_div(ticks, USEC_PER_SEC);
>> -		tegra_pmc_writel(pmc, ticks, PMC_CPUPWROFF_TIMER);
>> +	ticks = pmc->cpu_good_time * rate + USEC_PER_SEC - 1;
>> +	do_div(ticks, USEC_PER_SEC);
>> +	tegra_pmc_writel(pmc, ticks, PMC_CPUPWRGOOD_TIMER);
> 
> You could go a step further and update the cpu_good_time/cpu_off_time to
> be ticks and calculated once during probe and recalculated if
> tegra_pmc_set_suspend_mode is called. I am not sure why we really need
> to pass mode to tegra_pmc_enter_suspend_mode() seeing as the mode is
> stored in the pmc struct.
> 
>>  
>> -		wmb();
>> -
>> -		pmc->rate = rate;
>> -	}
>> +	ticks = pmc->cpu_off_time * rate + USEC_PER_SEC - 1;
>> +	do_div(ticks, USEC_PER_SEC);
>> +	tegra_pmc_writel(pmc, ticks, PMC_CPUPWROFF_TIMER);
>>  
>>  	value = tegra_pmc_readl(pmc, PMC_CNTRL);
>>  	value &= ~PMC_CNTRL_SIDE_EFFECT_LP0;
>>  	value |= PMC_CNTRL_CPU_PWRREQ_OE;
>>  	tegra_pmc_writel(pmc, value, PMC_CNTRL);
>> +
>> +	wmb();

I would not move the barrier unless there is a good reason. Maybe it is
intentional that this happens before the other writes.

Jon

-- 
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