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

[Bjorn Andersson <bjorn.andersson@linaro.org>]

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.

> +		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.

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
>