Re: [PATCH v3 4/7] clk: qcom: gdsc: call runtime PM functions for the provider device

[Dmitry Baryshkov <dmitry.baryshkov@linaro.org>]

On 09/07/2021 21:54, Bjorn Andersson wrote:
> On Fri 09 Jul 12:31 CDT 2021, Dmitry Baryshkov wrote:
> 
>> In order to properly handle runtime PM status of the provider device,
>> call pm_runtime_get/pm_runtime_put on the clock controller device.
>>
>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
>> ---
>>   drivers/clk/qcom/gdsc.c | 66 ++++++++++++++++++++++++++++++++++++++---
>>   drivers/clk/qcom/gdsc.h |  2 ++
>>   2 files changed, 64 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/clk/qcom/gdsc.c b/drivers/clk/qcom/gdsc.c
>> index ccd36617d067..6bec31fccb09 100644
>> --- a/drivers/clk/qcom/gdsc.c
>> +++ b/drivers/clk/qcom/gdsc.c
>> @@ -11,6 +11,7 @@
>>   #include <linux/kernel.h>
>>   #include <linux/ktime.h>
>>   #include <linux/pm_domain.h>
>> +#include <linux/pm_runtime.h>
>>   #include <linux/regmap.h>
>>   #include <linux/regulator/consumer.h>
>>   #include <linux/reset-controller.h>
>> @@ -50,6 +51,30 @@ enum gdsc_status {
>>   	GDSC_ON
>>   };
>>   
>> +static int gdsc_pm_runtime_get(struct gdsc *sc)
>> +{
>> +	int ret;
>> +
>> +	if (!sc->rpm_dev)
>> +		return 0;
>> +
>> +	ret = pm_runtime_get_sync(sc->rpm_dev);
>> +	if (ret < 0) {
>> +		pm_runtime_put_noidle(sc->rpm_dev);
>> +		return ret;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int gdsc_pm_runtime_put(struct gdsc *sc)
>> +{
>> +	if (!sc->rpm_dev)
>> +		return 0;
>> +
>> +	return pm_runtime_put_sync(sc->rpm_dev);
>> +}
>> +
>>   /* Returns 1 if GDSC status is status, 0 if not, and < 0 on error */
>>   static int gdsc_check_status(struct gdsc *sc, enum gdsc_status status)
>>   {
>> @@ -232,9 +257,8 @@ static void gdsc_retain_ff_on(struct gdsc *sc)
>>   	regmap_update_bits(sc->regmap, sc->gdscr, mask, mask);
>>   }
>>   
>> -static int gdsc_enable(struct generic_pm_domain *domain)
>> +static int _gdsc_enable(struct gdsc *sc)
>>   {
>> -	struct gdsc *sc = domain_to_gdsc(domain);
>>   	int ret;
>>   
>>   	if (sc->pwrsts == PWRSTS_ON)
>> @@ -290,11 +314,28 @@ static int gdsc_enable(struct generic_pm_domain *domain)
>>   	return 0;
>>   }
>>   
>> -static int gdsc_disable(struct generic_pm_domain *domain)
>> +static int gdsc_enable(struct generic_pm_domain *domain)
>>   {
>>   	struct gdsc *sc = domain_to_gdsc(domain);
>>   	int ret;
>>   
>> +	ret = gdsc_pm_runtime_get(sc);
>> +	if (ret)
>> +		return ret;
>> +
>> +	ret = _gdsc_enable(sc);
>> +	if (ret) {
>> +		gdsc_pm_runtime_put(sc);
> 
> I presume what you do here is to leave the pm_runtime state of dispcc
> active if we succeeded in enabling the gdsc. But the gdsc is a subdomain
> of the parent domain, so the framework should take case of its
> dependency.
> 
> So the reason for gdsc_pm_runtime_get()/put() in this code path is so
> that you can access the dispcc registers, i.e. I think you should
> get()/put() regardless of the return value.

pm domain code will handle enabling MMCX, so this code is not required 
strictly speaking. Ulf suggested adding it back, so I followed the 
suggestion. Maybe I misunderstood his suggestion.

putting pm_runtime after gdsc_enable does not sound like a logical case. 
However it would simplify code a bit. Let me try...

> 
>> +		return ret;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int _gdsc_disable(struct gdsc *sc)
>> +{
>> +	int ret;
>> +
>>   	if (sc->pwrsts == PWRSTS_ON)
>>   		return gdsc_assert_reset(sc);
>>   
>> @@ -329,6 +370,18 @@ static int gdsc_disable(struct generic_pm_domain *domain)
>>   	return 0;
>>   }
>>   
>> +static int gdsc_disable(struct generic_pm_domain *domain)
>> +{
>> +	struct gdsc *sc = domain_to_gdsc(domain);
>> +	int ret;
>> +
> 
> If the gdsc is found to be on at initialization, the next operation that
> will happen is gdsc_disable() and as you didn't activate the pm_runtime
> state in gdsc_init() you would in theory get here with registers
> unaccessible.
> 
> In practice though, the active gdsc should through the being a subdomain
> of the parent domain keep power on for you, so you won't notice this
> issue.

Nice catch.

> 
> But as above, I think you should wrap _gdsc_disable() in a get()/put()
> pair.
> 
>> +	ret = _gdsc_disable(sc);
>> +	if (ret)
>> +		return ret;
>> +
>> +	return gdsc_pm_runtime_put(sc);
>> +}
>> +
>>   static int gdsc_init(struct gdsc *sc)
>>   {
>>   	u32 mask, val;
>> @@ -425,6 +478,8 @@ int gdsc_register(struct gdsc_desc *desc,
>>   	for (i = 0; i < num; i++) {
>>   		if (!scs[i])
>>   			continue;
>> +		if (pm_runtime_enabled(dev))
>> +			scs[i]->rpm_dev = dev;
>>   		scs[i]->regmap = regmap;
>>   		scs[i]->rcdev = rcdev;
>>   		ret = gdsc_init(scs[i]);
>> @@ -486,7 +541,10 @@ void gdsc_unregister(struct gdsc_desc *desc)
>>    */
>>   int gdsc_gx_do_nothing_enable(struct generic_pm_domain *domain)
>>   {
>> +	struct gdsc *sc = domain_to_gdsc(domain);
>> +
>>   	/* Do nothing but give genpd the impression that we were successful */
>> -	return 0;
>> +	/* Get the runtime PM device only */
>> +	return gdsc_pm_runtime_get(sc);
> 
> Per above, if you let the framework deal with the gdsc's dependencies on
> the parent domain and you only get()/put() for the sake of dispcc then
> you don't need you don't need to do this to keep the subsequent
> gdsc_disable() in balance.
> 
>>   }
>>   EXPORT_SYMBOL_GPL(gdsc_gx_do_nothing_enable);
>> diff --git a/drivers/clk/qcom/gdsc.h b/drivers/clk/qcom/gdsc.h
>> index 5bb396b344d1..a82982df0a55 100644
>> --- a/drivers/clk/qcom/gdsc.h
>> +++ b/drivers/clk/qcom/gdsc.h
>> @@ -25,6 +25,7 @@ struct reset_controller_dev;
>>    * @resets: ids of resets associated with this gdsc
>>    * @reset_count: number of @resets
>>    * @rcdev: reset controller
>> + * @rpm_dev: runtime PM device
>>    */
>>   struct gdsc {
>>   	struct generic_pm_domain	pd;
>> @@ -58,6 +59,7 @@ struct gdsc {
>>   
>>   	const char 			*supply;
>>   	struct regulator		*rsupply;
>> +	struct device 			*rpm_dev;
> 
> This isn't just the "runtime pm device", it's the device this gdsc is
> associated with. So "dev" sounds sufficient to me, but that requires
> that you have a separate bool rpm_enabled to remember if
> pm_runtime_enabled() was true during probe.
> 
> So unless we need "dev" for something else this might be sufficient.
> 
> Regards,
> Bjorn
> 
>>   };
>>   
>>   struct gdsc_desc {
>> -- 
>> 2.30.2
>>


-- 
With best wishes
Dmitry