linux-kernel - Re: [PATCH 5/7] iio: light: veml6030: update sensor resolution

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Message-ID: <5199bc7c-c3fe-49e8-9122-78b476c4aa90@gmail.com>
Date: Sun, 15 Sep 2024 10:31:11 +0200
From: Javier Carrasco <javier.carrasco.cruz@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Rishi Gupta <gupt21@...il.com>,
 linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH 5/7] iio: light: veml6030: update sensor resolution

On 14/09/2024 16:57, Jonathan Cameron wrote:
> On Fri, 13 Sep 2024 15:19:00 +0200
> Javier Carrasco <javier.carrasco.cruz@...il.com> wrote:
> 
>> The driver still uses the sensor resolution provided in the datasheet
>> until Rev. 1.6, 28-Apr-2022, which was updated with Rev 1.7,
>> 28-Nov-2023. The original ambient light resolution has been updated from
>> 0.0036 lx/ct to 0.0042 lx/ct, which is the value that can be found in
>> the current device datasheet.
>>
>> Update the default resolution for IT = 100 ms and GAIN = 1/8 from the
>> original 4608 mlux/cnt to the current value from the "Resolution and
>> maximum detection range" table (Application Note 84367, page 5), 5376
>> mlux/cnt.
>>
>> Signed-off-by: Javier Carrasco <javier.carrasco.cruz@...il.com>
> Interesting.  So does the datasheet say this was fixing an error, or
> is there any chance there are different versions of the chip out there?
> 
> Also, should we treat this as a fix?  I think we probably should given
> we don't really want stable kernels to have wrong data being reported.
> If so, please reply with a fixes tag.
> 
> Jonathan
>

According to the Product Information Notification (link in the cover
letter):

"Reason for Change: Adjusted resolution as this was wrongly stated in
the current datasheet."

"If resolution is defined in the particular application by the customer,
no changes in the system should be made. In the case resolution was
taken from the datasheet or app note, this has to be adjusted accordingly."

Which means that stable kernels are using the wrong resolution. I don't
know what IIO usually does in such cases, because a fix could
potentially make existing applications return "wrong data". If that is
alright, and applications are meant to be adjusted after the kernel
update, I have no problems to make this patch as a fix and add the
stable tag.

Best regards,
Javier Carrasco

>> ---
>>  drivers/iio/light/veml6030.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/iio/light/veml6030.c b/drivers/iio/light/veml6030.c
>> index 5d4c2e35b987..d5add040d0b3 100644
>> --- a/drivers/iio/light/veml6030.c
>> +++ b/drivers/iio/light/veml6030.c
>> @@ -779,7 +779,7 @@ static int veml6030_hw_init(struct iio_dev *indio_dev)
>>  
>>  	/* Cache currently active measurement parameters */
>>  	data->cur_gain = 3;
>> -	data->cur_resolution = 4608;
>> +	data->cur_resolution = 5376;
>>  	data->cur_integration_time = 3;
>>  
>>  	return ret;
>>
>