Re: [PATCH v2 2/4] media: v4l2-common: Add kernel-doc for v4l2_fill_pixfmt_mp_aligned()

[Sven Püschel]

Hi Tommaso,

thanks for adding documentation.

On 7/1/26 6:49 PM, Tommaso Merciai wrote:
> Replace the bare placeholder comment with a full kernel-doc block
> documenting all parameters, the function behaviour for both single
> memory plane (mem_planes == 1) and multiple memory plane (mem_planes > 1)
> formats, and the return value.
>
> Signed-off-by: Tommaso Merciai<tommaso.merciai.xr@xxxxxxxxxxxxxx>
> ---
> v1->v2:
>   - New patch
>
>   include/media/v4l2-common.h | 27 ++++++++++++++++++++++++++-
>   1 file changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h
> index 749fe38c134e..db59dda578f0 100644
> --- a/include/media/v4l2-common.h
> +++ b/include/media/v4l2-common.h
> @@ -557,7 +557,32 @@ void v4l2_apply_frmsize_constraints(u32 *width, u32 *height,
>   int v4l2_fill_pixfmt(struct v4l2_pix_format *pixfmt, u32 pixelformat,
>   		     u32 width, u32 height);
>   
> -/* @stride_alignment is a power of 2 value in bytes */
> +/**
> + * v4l2_fill_pixfmt_mp_aligned - Fill in a &struct v4l2_pix_format_mplane with
> + *	stride alignment requirements.
> + *
> + * @pixfmt: pointer to the &struct v4l2_pix_format_mplane to be filled
> + * @pixelformat: the V4L2 pixel format (V4L2_PIX_FMT_*)
> + * @width: image width in pixels
> + * @height: image height in pixels
> + * @stride_alignment: stride alignment in bytes; must be a power of 2
> + *
> + * Fills all fields of @pixfmt for the given pixel format, dimensions, and
> + * stride alignment.
> + *
> + * For formats stored in a single memory plane (mem_planes == 1), the
> + * behaviour matches v4l2_fill_pixfmt_aligned(): plane_fmt[0].bytesperline
Given that the v4l2_fill_pixfmt_aligned helper is added later in patch 
3, don't you want to move this patch after adding the helper?
> + * is set to the primary plane stride rounded up to @stride_alignment, and
> + * per-component alignments are scaled to keep chroma strides consistently
> + * derivable from the luma stride. plane_fmt[0].sizeimage covers all

No, it's the other way: The strides of all components are aligned to the 
@stride_alignment. To keep the chroma strides consistently derivable 
from the luma stride, strides may be aligned to a multiple of the 
@stride_alignment.

(feel free to use the above if it sounds good)

At least I read your text, as if only the y stride would be rounded up 
to the nearest alignment and for other component strides may be scaled 
down to 1/2 or 1/4 of the alignment. But most of the time the y stride 
will be scaled up (e.g. YUV420 or YUV410) and in rare cases (e.g. 
NV24/42) the component stride is scaled up.

Sincerely
    Sven

> + * component planes.
> + *
> + * For formats with multiple memory planes (mem_planes > 1), each plane's
> + * bytesperline is independently rounded up to @stride_alignment, and
> + * sizeimage is set to bytesperline multiplied by the plane height.
> + *
> + * Return: 0 on success, -EINVAL if @pixelformat is unknown.
> + */
>   int v4l2_fill_pixfmt_mp_aligned(struct v4l2_pix_format_mplane *pixfmt,
>   				u32 pixelformat, u32 width, u32 height,
>   				u8 stride_alignment);