[v1] soc/tegra: pmc: Query PCLK clock rate at probe time
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Message ID 20190707230843.11224-1-digetx@gmail.com
State New
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  • [v1] soc/tegra: pmc: Query PCLK clock rate at probe time
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Commit Message

Dmitry Osipenko July 7, 2019, 11:08 p.m. UTC
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.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
 drivers/soc/tegra/pmc.c | 26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)

Comments

Jon Hunter July 18, 2019, 9:45 a.m. UTC | #1
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@gmail.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();
>  }
>  #endif
>  
> @@ -2082,6 +2077,7 @@ static int tegra_pmc_probe(struct platform_device *pdev)
>  		pmc->clk = NULL;
>  	}
>  
> +	pmc->rate = clk_get_rate(pmc->clk);

You should check the value returned is not 0 here.

Cheers
Jon
Jon Hunter July 18, 2019, 9:53 a.m. UTC | #2
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@gmail.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
Dmitry Osipenko July 18, 2019, 6:12 p.m. UTC | #3
18.07.2019 12:45, Jon Hunter пишет:
> 
> 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.

Okay.

>> Signed-off-by: Dmitry Osipenko <digetx@gmail.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.

Indeed!

>>  		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.

The mode will differ depending on the idling mode. The system suspend
could be LP1, while CPUIDLE is LP2. Hence the mode need to be
reconfigured dynamically and thus the ticks.

>>  
>> -		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();
>>  }
>>  #endif
>>  
>> @@ -2082,6 +2077,7 @@ static int tegra_pmc_probe(struct platform_device *pdev)
>>  		pmc->clk = NULL;
>>  	}
>>  
>> +	pmc->rate = clk_get_rate(pmc->clk);
> 
> You should check the value returned is not 0 here.

Good point!
Dmitry Osipenko July 18, 2019, 6:24 p.m. UTC | #4
18.07.2019 12:53, Jon Hunter пишет:
> 
> 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@gmail.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.

Looking at 'git blame', the barrier was copied by Thierry while he moved
PMC driver form mach-tegra/ to soc/. Originally the barrier appeared in
d552920a02759cdc45d8507868de10ac2f5b9a18 (ARM: tegra30: cpuidle: add
powered-down state for CPU0).

But really there is no good justification for that barrier at all
because PMC logic kicks-in when CPU enters power-gated state and at that
point all CPU accesses guaranteed to be finished no matter what, hence
this barrier just doesn't make much sense and can be removed safely.
I'll make a separate commit for that.
Peter De Schrijver July 25, 2019, 9:41 a.m. UTC | #5
On Thu, Jul 18, 2019 at 10:45:31AM +0100, 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.
> 

SCLK and PCLK certainly can change rate at runtime, although the changes
for this haven't made it upstream yet. It's indeed not very obvious, but
certainly doable.

Peter.

Patch
diff mbox series

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;
 		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);
 
-		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();
 }
 #endif
 
@@ -2082,6 +2077,7 @@  static int tegra_pmc_probe(struct platform_device *pdev)
 		pmc->clk = NULL;
 	}
 
+	pmc->rate = clk_get_rate(pmc->clk);
 	pmc->dev = &pdev->dev;
 
 	tegra_pmc_init(pmc);