linux-kernel - Re: [PATCH] iio: light: apds9306: fix max_scale

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Message-ID: <ad1b01ba-53c0-4adf-aee4-a9bc0ff88ae0@tweaklogic.com>
Date: Thu, 16 Jan 2025 22:04:01 +1030
From: Subhajit Ghosh <subhajit.ghosh@...aklogic.com>
To: Javier Carrasco <javier.carrasco.cruz@...il.com>,
 Jonathan Cameron <jic23@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>, stable@...r.kernel.org
Subject: Re: [PATCH] iio: light: apds9306: fix max_scale_nano values

On 12/1/25 10:38, Javier Carrasco wrote:
> The two provided max_scale_nano values must be multiplied by 100 and 10
> respectively to achieve nano units. According to the comments:
> 
> Max scale for apds0306 is 16.326432 → the fractional part is 0.326432,
> which is 326432000 in NANO. The current value is 3264320.
> 
> Max scale for apds0306-065 is 14.09721 → the fractional part is 0.09712,
> which is 97120000 in NANO. The current value is 9712000.
> 
> Update max_scale_nano initialization to use the right NANO fractional
> parts.
> 
> Cc: stable@...r.kernel.org
> Fixes: 620d1e6c7a3f ("iio: light: Add support for APDS9306 Light Sensor")
> Signed-off-by: Javier Carrasco <javier.carrasco.cruz@...il.com>
> ---
>   drivers/iio/light/apds9306.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/light/apds9306.c b/drivers/iio/light/apds9306.c
> index 69a0d609cffc91cc3daba160f309f511270be385..5ed7e17f49e76206609aba83c85e8144c536d17d 100644
> --- a/drivers/iio/light/apds9306.c
> +++ b/drivers/iio/light/apds9306.c
> @@ -108,11 +108,11 @@ static const struct part_id_gts_multiplier apds9306_gts_mul[] = {
>   	{
>   		.part_id = 0xB1,
>   		.max_scale_int = 16,
> -		.max_scale_nano = 3264320,
> +		.max_scale_nano = 326432000,
>   	}, {
>   		.part_id = 0xB3,
>   		.max_scale_int = 14,
> -		.max_scale_nano = 9712000,
> +		.max_scale_nano = 97120000,
>   	},
>   };
>   
> 
> ---
> base-commit: 577a66e2e634f712384c57a98f504c44ea4b47da
> change-id: 20241218-apds9306_nano_vals-d880219a82f2
> 
> Best regards,
Hi Javier,

You are correct.
  From iio_gts_linearize() function in industrialio-gts-helper.c
*lin_scale = (u64)scale_whole * (u64)scaler + (u64)(scale_nano / (NANO / scaler));
where "scaler" equals NANO (1000000000UL)

I tested it, no issues. The values did not deviate much as this is nano scale.

Tested-by: subhajit.ghosh@...aklogic.com

Regards,
Subhajit Ghosh