Re: [PATCH 07/14] iio: adc: rzg2l_adc: Enable runtime PM autosuspend support

Claudiu Beznea
2024-12-04T08:31:40Z

Hi, Jonathan,

On 03.12.2024 22:00, Jonathan Cameron wrote:
> On Tue, 3 Dec 2024 13:13:07 +0200
> Claudiu <claudiu.beznea@tuxon.dev> wrote:
>
>> From: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>>
>> Enable runtime PM autosuspend support for the rzg2l_adc driver. With this
>> change, consecutive conversion requests will no longer cause the device to
>> be runtime-enabled/disabled after each request. Instead, the device will
>> transition based on the delay configured by the user.
>>
>> This approach reduces the frequency of hardware register access during
>> runtime PM suspend/resume cycles, thereby saving CPU cycles. The default
>> autosuspend delay is set to zero to maintain the previous driver behavior.
>
> Unless you have a weird user who is polling slow enough to not trigger
> autosuspend with a non zero period, but is still saving power I'm not convinced
> anyone will notice if you just enable this for a sensible autosuspend delay.
> There will of course be a small increase in power usage for each read but
> hopefully that is trivial.
>
> So I'd not go with a default of 0, though what value makes sense depends
> on the likely usecase + how much power is saved by going to sleep.
>
> If you really want to keep 0 I don't mind that much, just seems odd!

I agree with you. I chose it like this as I got internal request (on other
drivers enabling autosuspend support) to keep the previous behavior in place.

Thank you for your review,
Claudiu

>
> Jonathan
>
>>
>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>> ---
>> drivers/iio/adc/rzg2l_adc.c | 9 +++++++--
>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/iio/adc/rzg2l_adc.c b/drivers/iio/adc/rzg2l_adc.c
>> index eed2944bd98d..fda8b42ded81 100644
>> --- a/drivers/iio/adc/rzg2l_adc.c
>> +++ b/drivers/iio/adc/rzg2l_adc.c
>> @@ -207,7 +207,8 @@ static int rzg2l_adc_conversion(struct iio_dev *indio_dev, struct rzg2l_adc *adc
>> rzg2l_adc_start_stop(adc, false);
>>
>> rpm_put:
>> - pm_runtime_put_sync(dev);
>> + pm_runtime_mark_last_busy(dev);
>> + pm_runtime_put_autosuspend(dev);
>> return ret;
>> }
>>
>> @@ -372,7 +373,8 @@ static int rzg2l_adc_hw_init(struct device *dev, struct rzg2l_adc *adc)
>> rzg2l_adc_writel(adc, RZG2L_ADM(3), reg);
>>
>> exit_hw_init:
>> - pm_runtime_put_sync(dev);
>> + pm_runtime_mark_last_busy(dev);
>> + pm_runtime_put_autosuspend(dev);
>> return ret;
>> }
>>
>> @@ -412,6 +414,9 @@ static int rzg2l_adc_probe(struct platform_device *pdev)
>> return PTR_ERR(adc->presetn);
>> }
>>
>> + /* Default 0 for power saving. Can be overridden via sysfs. */
>> + pm_runtime_set_autosuspend_delay(dev, 0);
>> + pm_runtime_use_autosuspend(dev);
>> ret = devm_pm_runtime_enable(dev);
>> if (ret)
>> return ret;
>