On 5/3/20 1:48 PM, Jonathan Cameron wrote:
> On Wed, 29 Apr 2020 14:29:08 +0200
> Fabrice Gasnier <fabrice.gasnier@xxxxxx> 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@xxxxxx>
>
> 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 = {
>
