Re: [PATCH v2 10/10] media: microchip-isc: fix WB offset and gain register field masking

[Eugen Hristev <ehristev@kernel.org>]

On 6/29/26 14:09, Balakrishnan Sambath wrote:
> ISC_WB_O_* and ISC_WB_G_* pack two 13-bit fields per register. Sign
> extension from negative offsets corrupts the upper field. Mask both
> fields to 13 bits before packing.
> 
> Fixes: 91b4e487b0c6 ("media: microchip: add ISC driver as Microchip ISC")
> Cc: stable@vger.kernel.org
> Signed-off-by: Balakrishnan Sambath <balakrishnan.s@microchip.com>
> ---
>  .../media/platform/microchip/microchip-isc-base.c  | 22 ++++++++++++++--------
>  1 file changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/media/platform/microchip/microchip-isc-base.c b/drivers/media/platform/microchip/microchip-isc-base.c
> index 1a9b97edfa32..79a58efb6333 100644
> --- a/drivers/media/platform/microchip/microchip-isc-base.c
> +++ b/drivers/media/platform/microchip/microchip-isc-base.c
> @@ -62,18 +62,24 @@ static inline void isc_update_awb_ctrls(struct isc_device *isc)
>  
>  	/* In here we set our actual hw pipeline config */
>  
> +	/*
> +	 * Offsets are 13-bit signed fields [12:0] and [28:16]. Cast to
> +	 * u32 and mask to 13 bits so sign extension of a negative value
> +	 * cannot corrupt the adjacent field.
> +	 */
>  	regmap_write(isc->regmap, ISC_WB_O_RGR,
> -		     ((ctrls->offset[ISC_HIS_CFG_MODE_R])) |
> -		     ((ctrls->offset[ISC_HIS_CFG_MODE_GR]) << 16));
> +		     ((u32)ctrls->offset[ISC_HIS_CFG_MODE_R] & GENMASK(12, 0)) |
> +		     (((u32)ctrls->offset[ISC_HIS_CFG_MODE_GR] & GENMASK(12, 0)) << 16));
>  	regmap_write(isc->regmap, ISC_WB_O_BGB,
> -		     ((ctrls->offset[ISC_HIS_CFG_MODE_B])) |
> -		     ((ctrls->offset[ISC_HIS_CFG_MODE_GB]) << 16));
> +		     ((u32)ctrls->offset[ISC_HIS_CFG_MODE_B] & GENMASK(12, 0)) |
> +		     (((u32)ctrls->offset[ISC_HIS_CFG_MODE_GB] & GENMASK(12, 0)) << 16));
> +	/* Gains are 13-bit unsigned fields [12:0] and [28:16] */
>  	regmap_write(isc->regmap, ISC_WB_G_RGR,
> -		     ctrls->gain[ISC_HIS_CFG_MODE_R] |
> -		     (ctrls->gain[ISC_HIS_CFG_MODE_GR] << 16));
> +		     (ctrls->gain[ISC_HIS_CFG_MODE_R] & GENMASK(12, 0)) |
> +		     ((ctrls->gain[ISC_HIS_CFG_MODE_GR] & GENMASK(12, 0)) << 16));
>  	regmap_write(isc->regmap, ISC_WB_G_BGB,
> -		     ctrls->gain[ISC_HIS_CFG_MODE_B] |
> -		     (ctrls->gain[ISC_HIS_CFG_MODE_GB] << 16));
> +		     (ctrls->gain[ISC_HIS_CFG_MODE_B] & GENMASK(12, 0)) |
> +		     ((ctrls->gain[ISC_HIS_CFG_MODE_GB] & GENMASK(12, 0)) << 16));
>  }
>  

Do you think you can rewrite these using FIELD_PREP ? It's getting a
little complicated to understand what is being written here.


>  static inline void isc_reset_awb_ctrls(struct isc_device *isc)
>