Re: [PATCH v3 3/7] clk: qcom: gdsc: enable optional power domain support

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

On 09/07/2021 21:38, Bjorn Andersson wrote:
> On Fri 09 Jul 12:31 CDT 2021, Dmitry Baryshkov wrote:
> 
>> On sm8250 dispcc and videocc registers are powered up by the MMCX power
>> domain. Currently we use a regulator to enable this domain on demand,
>> however this has some consequences, as genpd code is not reentrant.
>>
>> Teach Qualcomm clock controller code about setting up runtime PM and
>> using specified for gdsc powerup.
>>
>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
>> ---
>>   drivers/clk/qcom/common.c | 37 +++++++++++++++++++++++++++++++------
>>   drivers/clk/qcom/gdsc.c   |  4 ++++
>>   2 files changed, 35 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/clk/qcom/common.c b/drivers/clk/qcom/common.c
>> index 60d2a78d1395..43d8f8feeb3c 100644
>> --- a/drivers/clk/qcom/common.c
>> +++ b/drivers/clk/qcom/common.c
>> @@ -10,6 +10,7 @@
>>   #include <linux/clk-provider.h>
>>   #include <linux/reset-controller.h>
>>   #include <linux/of.h>
>> +#include <linux/pm_runtime.h>
>>   
>>   #include "common.h"
>>   #include "clk-rcg.h"
>> @@ -224,6 +225,11 @@ static struct clk_hw *qcom_cc_clk_hw_get(struct of_phandle_args *clkspec,
>>   	return cc->rclks[idx] ? &cc->rclks[idx]->hw : NULL;
>>   }
>>   
>> +static void qcom_cc_pm_runtime_disable(void *data)
>> +{
>> +	pm_runtime_disable(data);
>> +}
>> +
>>   int qcom_cc_really_probe(struct platform_device *pdev,
>>   			 const struct qcom_cc_desc *desc, struct regmap *regmap)
>>   {
>> @@ -241,6 +247,18 @@ int qcom_cc_really_probe(struct platform_device *pdev,
>>   	if (!cc)
>>   		return -ENOMEM;
>>   
>> +	pm_runtime_enable(dev);
> 
> In turingcc-qcs404.c I'm using pm_runtime to have the clock framework
> ensure that the iface clock is enabled during clock operations, so this
> will result in a "unbalanced enable" warning.

And later I register the disabler:

  ret = devm_add_action_or_reset(dev, qcom_cc_pm_runtime_disable, dev);

You might want to add this to qcs404 code.

> 
>> +	ret = pm_runtime_get_sync(dev);
> 
> I don't think you should wrap the entire initialization in a
> pm_runtime_get_sync()/put() region. Instead follow the clock framework
> and wrap gdsc initialization that needs to touch the hardware in:

Init should be wrapped in the pm_runtime_get/put calls, so that the MMCX 
domain is on through the fall init sequence. Otherwise it can get turned 
off during it, boom, failed register access and reboot.

> 
> 	if (pm_runtime_enabled())
> 		pm_runtime_get_sync();

I don't think it's worth doing that. Having single lock for the whole 
init sequence is safer (and cleaner).

If you check other pm-enabled drivers, they would either call 
pm_runtime_enable at the end of the probe or get_sync in the beginning 
of the probe and put_FOO in the end. In this driver calling 
pm_runtime_enable() at the end of the probe function will not work, 
since this way clk subsystem will not pick up the device for runtime 
power management (as pm_runtime_enabled() would return false).

> 
> I do however think that as of this patch, when probe returns MMCX might
> very well be turned off, as the only user (this driver) has pm_runtime
> enabled and it's idle. So I think you should introduce the
> pm_runtime_get()/put() in the gdsc functions before this patch.

Maybe I'd just squash them together.

> 
> 
> To summarize, I think you should rely on the individual clock drivers to
> pm_runtime_enable()/disable().
> 
>> +	if (ret < 0) {
>> +		pm_runtime_put(dev);
>> +		pm_runtime_disable(dev);
>> +		return ret;
>> +	}
>> +
>> +	ret = devm_add_action_or_reset(dev, qcom_cc_pm_runtime_disable, dev);
>> +	if (ret)
>> +		goto err;
>> +
>>   	reset = &cc->reset;
>>   	reset->rcdev.of_node = dev->of_node;
>>   	reset->rcdev.ops = &qcom_reset_ops;
>> @@ -251,7 +269,7 @@ int qcom_cc_really_probe(struct platform_device *pdev,
>>   
>>   	ret = devm_reset_controller_register(dev, &reset->rcdev);
>>   	if (ret)
>> -		return ret;
>> +		goto err;
>>   
>>   	if (desc->gdscs && desc->num_gdscs) {
>>   		scd = devm_kzalloc(dev, sizeof(*scd), GFP_KERNEL);
>> @@ -262,11 +280,11 @@ int qcom_cc_really_probe(struct platform_device *pdev,
>>   		scd->num = desc->num_gdscs;
>>   		ret = gdsc_register(scd, &reset->rcdev, regmap);
>>   		if (ret)
>> -			return ret;
>> +			goto err;
>>   		ret = devm_add_action_or_reset(dev, qcom_cc_gdsc_unregister,
>>   					       scd);
>>   		if (ret)
>> -			return ret;
>> +			goto err;
>>   	}
>>   
>>   	cc->rclks = rclks;
>> @@ -277,7 +295,7 @@ int qcom_cc_really_probe(struct platform_device *pdev,
>>   	for (i = 0; i < num_clk_hws; i++) {
>>   		ret = devm_clk_hw_register(dev, clk_hws[i]);
>>   		if (ret)
>> -			return ret;
>> +			goto err;
>>   	}
>>   
>>   	for (i = 0; i < num_clks; i++) {
>> @@ -286,14 +304,21 @@ int qcom_cc_really_probe(struct platform_device *pdev,
>>   
>>   		ret = devm_clk_register_regmap(dev, rclks[i]);
>>   		if (ret)
>> -			return ret;
>> +			goto err;
>>   	}
>>   
>>   	ret = devm_of_clk_add_hw_provider(dev, qcom_cc_clk_hw_get, cc);
>>   	if (ret)
>> -		return ret;
>> +		goto err;
>> +
>> +	pm_runtime_put(dev);
>>   
>>   	return 0;
>> +
>> +err:
>> +	pm_runtime_put(dev);
>> +
>> +	return ret;
>>   }
>>   EXPORT_SYMBOL_GPL(qcom_cc_really_probe);
>>   
>> diff --git a/drivers/clk/qcom/gdsc.c b/drivers/clk/qcom/gdsc.c
>> index 51ed640e527b..ccd36617d067 100644
>> --- a/drivers/clk/qcom/gdsc.c
>> +++ b/drivers/clk/qcom/gdsc.c
>> @@ -439,6 +439,8 @@ int gdsc_register(struct gdsc_desc *desc,
>>   			continue;
>>   		if (scs[i]->parent)
>>   			pm_genpd_add_subdomain(scs[i]->parent, &scs[i]->pd);
>> +		else if (!IS_ERR_OR_NULL(dev->pm_domain))
>> +			pm_genpd_add_subdomain(pd_to_genpd(dev->pm_domain), &scs[i]->pd);
> 
> Nice, I didn't know that we could fish it out of the dev.
> 
> Regards,
> Bjorn
> 
>>   	}
>>   
>>   	return of_genpd_add_provider_onecell(dev->of_node, data);
>> @@ -457,6 +459,8 @@ void gdsc_unregister(struct gdsc_desc *desc)
>>   			continue;
>>   		if (scs[i]->parent)
>>   			pm_genpd_remove_subdomain(scs[i]->parent, &scs[i]->pd);
>> +		else if (!IS_ERR_OR_NULL(dev->pm_domain))
>> +			pm_genpd_remove_subdomain(pd_to_genpd(dev->pm_domain), &scs[i]->pd);
>>   	}
>>   	of_genpd_del_provider(dev->of_node);
>>   }
>> -- 
>> 2.30.2
>>


-- 
With best wishes
Dmitry