Re: [PATCH v4 1/2] media: atomisp: csi2: Remove unimplemented DPCM decompression

[Sakari Ailus]

Hi Debjeet,

On Wed, Apr 22, 2026 at 05:50:05PM +0530, Debjeet Banerjee wrote:
> The source pad format handling attempted to map DPCM-compressed mbus
> codes to their uncompressed equivalents. However, the rest of the
> driver does not support DPCM decompression, making this dead code.
> 
> Remove the DPCM unmapping logic and simplify to directly copy the sink
> pad format to the source pad. Add an explicit comment stating that
> DPCM is not supported.
> 
> Signed-off-by: Debjeet Banerjee <debjeetbanerjee48@xxxxxxxxx>
> ---
> v4:
> - Complete removal of DPCM decompression attempt (per Sakari Ailus feedback)
> - Keep source pad simply copying sink pad format without unmapping
> - Replace detailed comment with explicit "DPCM is not supported" statement
> 
> v3:
> - Drop "staging:" prefix in subject (per Andy Shevchenko)
> 
> v2:
> - Rebased onto latest media tree (fix CI apply failure)
> - Fix missing linux-staging recipient (typo in v1)
> - Fix indentation
> ---
>  drivers/staging/media/atomisp/pci/atomisp_csi2.c | 15 ++++-----------
>  1 file changed, 4 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/staging/media/atomisp/pci/atomisp_csi2.c b/drivers/staging/media/atomisp/pci/atomisp_csi2.c
> index e723304bec80..64419c1a805e 100644
> --- a/drivers/staging/media/atomisp/pci/atomisp_csi2.c
> +++ b/drivers/staging/media/atomisp/pci/atomisp_csi2.c
> @@ -107,17 +107,10 @@ int atomisp_csi2_set_ffmt(struct v4l2_subdev *sd,
>  					     &tmp_ffmt);
>  	}
>  
> -	/*
> -	 * The source pad must expose the uncompressed format even when the sink
> -	 * pad receives DPCM-compressed data. The hardware decompresses DPCM
> -	 * (e.g. SGRBG10_DPCM8_1X8 -> SGRBG10_1X10) between sink and source,
> -	 * so propagate the sink format but map the mbus code to its uncompressed
> -	 * equivalent. atomisp_subdev_uncompressed_code() returns the code
> -	 * unchanged for formats that are not DPCM-compressed.
> -	 */
> -	*actual_ffmt = *__csi2_get_format(csi2, sd_state, which, CSI2_PAD_SINK);
> -	actual_ffmt->code = atomisp_subdev_uncompressed_code(actual_ffmt->code);
> -	*ffmt = *actual_ffmt;

This won't apply to my atomisp branch.

> +	/* Source pad format is copied from sink pad. DPCM is not supported. */
> +	*actual_ffmt = *ffmt = *__csi2_get_format(csi2, sd_state, which,
> +						  CSI2_PAD_SINK);
> +
>  	return 0;
>  }
>  

-- 
Regards,

Sakari Ailus