linux-kernel - Re: [PATCH v2] iio: adc: stm32-adc: fix runtime autosuspend delay when slow polling

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Date:   Thu, 11 Jun 2020 12:09:12 +0200
From:   Fabrice Gasnier <fabrice.gasnier@...com>
To:     Jonathan Cameron <jic23@...nel.org>, <rjw@...ysocki.net>,
        <ulf.hansson@...aro.org>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <mcoquelin.stm32@...il.com>,
        <benjamin.gaignard@...com>, <alexandre.torgue@...com>,
        <olivier.moysan@...com>, <linux-iio@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>
Subject: Re: [PATCH v2] iio: adc: stm32-adc: fix runtime autosuspend delay
 when slow polling

On 5/3/20 1:48 PM, Jonathan Cameron wrote:
> On Wed, 29 Apr 2020 14:29:08 +0200
> Fabrice Gasnier <fabrice.gasnier@...com> wrote:
> 
>> When the ADC is runtime suspended and starting a conversion, the stm32-adc
>> driver calls pm_runtime_get_sync() that gets cascaded to the parent
>> (e.g. runtime resume of stm32-adc-core driver). This also kicks the
>> autosuspend delay (e.g. 2s) of the parent.
>> Once the ADC is active, calling pm_runtime_get_sync() again (upon a new
>> capture) won't kick the autosuspend delay for the parent (stm32-adc-core
>> driver) as already active.
>>
>> Currently, this makes the stm32-adc-core driver go in suspend state
>> every 2s when doing slow polling. As an example, doing a capture, e.g.
>> cat in_voltageY_raw at a 0.2s rate, the auto suspend delay for the parent
>> isn't refreshed. Once it expires, the parent immediately falls into
>> runtime suspended state, in between two captures, as soon as the child
>> driver falls into runtime suspend state:
>> - e.g. after 2s, + child calls pm_runtime_put_autosuspend() + 100ms
>>   autosuspend delay of the child.
>> - stm32-adc-core switches off regulators, clocks and so on.
>> - They get switched on back again 100ms later in this example (at 2.2s).
>>
>> So, use runtime_idle() callback in stm32-adc-core driver to call
>> pm_runtime_mark_last_busy() for the parent driver (stm32-adc-core),
>> to avoid this.
>>
>> Fixes: 9bdbb1139ca1 ("iio: adc: stm32-adc: add power management support")
>>
>> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...com>
> 
> Whilst this seems 'sensible' to me, I really don't have a good enough grasp
> of runtime pm to be sure. 
> 
> I see something similar looking in the greybus driver, but not sure on the
> reason it is there.
> 
> Hence, ideally looking for an ack from Rafael on this one!

Hi,

Gentle reminder, I'm not sure how to progress on this patch.

Rafael, or maybe Ulf, could take a look at it ?

Thanks in advance,
Best Regards,
Fabrice

> 
> Thanks,
> 
> Jonathan
> 
>> ---
>> Changes in v2:
>> - Use runtime_idle callback in stm32-adc-core driver, instead of refreshing
>>   last_busy from the child (for the parent) at many place. Initial patch v1
>>   looked like "somewhat adhoc solution" as commented by Jonathan.
>> ---
>>  drivers/iio/adc/stm32-adc-core.c | 9 ++++++++-
>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iio/adc/stm32-adc-core.c b/drivers/iio/adc/stm32-adc-core.c
>> index 2df88d2..ebe5dbc 100644
>> --- a/drivers/iio/adc/stm32-adc-core.c
>> +++ b/drivers/iio/adc/stm32-adc-core.c
>> @@ -803,6 +803,13 @@ static int stm32_adc_core_runtime_resume(struct device *dev)
>>  {
>>  	return stm32_adc_core_hw_start(dev);
>>  }
>> +
>> +static int stm32_adc_core_runtime_idle(struct device *dev)
>> +{
>> +	pm_runtime_mark_last_busy(dev);
>> +
>> +	return 0;
>> +}
>>  #endif
>>  
>>  static const struct dev_pm_ops stm32_adc_core_pm_ops = {
>> @@ -810,7 +817,7 @@ static const struct dev_pm_ops stm32_adc_core_pm_ops = {
>>  				pm_runtime_force_resume)
>>  	SET_RUNTIME_PM_OPS(stm32_adc_core_runtime_suspend,
>>  			   stm32_adc_core_runtime_resume,
>> -			   NULL)
>> +			   stm32_adc_core_runtime_idle)
>>  };
>>  
>>  static const struct stm32_adc_priv_cfg stm32f4_adc_priv_cfg = {
>