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

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Message-ID: <e05191b0-eb3b-472f-bd8f-9d9a28100d0a@tuxon.dev>
Date: Wed, 4 Dec 2024 10:31:36 +0200
From: Claudiu Beznea <claudiu.beznea@...on.dev>
To: Jonathan Cameron <jic23@...nel.org>
Cc: prabhakar.mahadev-lad.rj@...renesas.com, lars@...afoo.de,
 robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 geert+renesas@...der.be, magnus.damm@...il.com, mturquette@...libre.com,
 sboyd@...nel.org, p.zabel@...gutronix.de, linux-iio@...r.kernel.org,
 linux-renesas-soc@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH 07/14] iio: adc: rzg2l_adc: Enable runtime PM autosuspend
 support

Hi, Jonathan,

On 03.12.2024 22:00, Jonathan Cameron wrote:
> On Tue,  3 Dec 2024 13:13:07 +0200
> Claudiu <claudiu.beznea@...on.dev> wrote:
> 
>> From: Claudiu Beznea <claudiu.beznea.uj@...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@...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;
>