Re: [PATCH v1 1/4] iio: light: opt4001: Fix read-modify-write of wrong register in power down

[Nikhil Gautam <nikhilgtr@gmail.com>]

On 13-07-2026 06:12 am, Jonathan Cameron wrote:
> On Mon, 13 Jul 2026 01:54:48 +0530
> Nikhil Gautam <nikhilgtr@gmail.com> wrote:
>
>> opt4001_power_down() intends to clear the operating mode bits in the
>> CTRL register but reads OPT4001_DEVICE_ID instead of OPT4001_CTRL.
>> The device ID value with the mode bits masked out is then written to
>> CTRL, corrupting the conversion time and fault count configuration.
>>
>> Read the CTRL register instead so only the operating mode bits are
>> cleared and the rest of the configuration is preserved.
>>
>> Signed-off-by: Nikhil Gautam <nikhilgtr@gmail.com>
> Fixes tag please (you asked in the cover letter and yes it is appropriate
> even though these go all the way back).
>
> Looks correct but I think we can take this opportunity to simplify
> the code whilst fixing the issue.
Sure, will add Fixes tags.
>> ---
>>   drivers/iio/light/opt4001.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/iio/light/opt4001.c b/drivers/iio/light/opt4001.c
>> index ba4eb82d9bc2..f2cf496cc243 100644
>> --- a/drivers/iio/light/opt4001.c
>> +++ b/drivers/iio/light/opt4001.c
>> @@ -228,7 +228,7 @@ static int opt4001_power_down(struct opt4001_chip *chip)
>>   	int ret;
>>   	unsigned int reg;
>>   
>> -	ret = regmap_read(chip->regmap, OPT4001_DEVICE_ID, &reg);
>> +	ret = regmap_read(chip->regmap, OPT4001_CTRL, &reg);
> Let us jump directly to a regmap_clear_bits()
>
> It will fix this issue and generally improve the code readabilty.
>
> Given this is only called in one place and the code will be nearly a one liner
> after that change, lets also just  move it directly into opt3001_chip_power_off_action().
>
> I my opinion all that is just about fine in a single fix patch, rather than a
> separate fix + code cleanup to follow, but if you would rather split it up into
> fix first then refactor I don't mind.  I may well decide to mere this whole series
> for the next merge window anyway just to ensure it all makes it reasonably quickly
> (at expensive of the fixes making it in a little faster and possibly delaying any
> cleanup).
>
> Thanks,
>
> Jonathan
>
Agreed, that is much cleaner. I will move the regmap_clear_bits() call
directly into the devm action and drop opt4001_power_down() as a single
fix patch in v2, with the Fixes tag added.

Thanks,
Nikhil