Re: [PATCH 1/3] drm/draw: add drm_draw_can_convert_from_xrgb8888

[Jani Nikula <jani.nikula@linux.intel.com>]

On Sun, 05 Oct 2025, Francesco Valla <francesco@valla.it> wrote:
> Add drm_draw_can_convert_from_xrgb8888() function that can be used to
> determine if a XRGB8888 color can be converted to the specified format.
>
> Signed-off-by: Francesco Valla <francesco@valla.it>
> ---
>  drivers/gpu/drm/drm_draw.c          | 84 +++++++++++++++++++++++++++----------
>  drivers/gpu/drm/drm_draw_internal.h |  2 +
>  2 files changed, 63 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_draw.c b/drivers/gpu/drm/drm_draw.c
> index 9dc0408fbbeadbe8282a2d6b210e0bfb0672967f..2641026a103d3b28cab9f5d378604b0604520fe4 100644
> --- a/drivers/gpu/drm/drm_draw.c
> +++ b/drivers/gpu/drm/drm_draw.c
> @@ -15,45 +15,83 @@
>  #include "drm_draw_internal.h"
>  #include "drm_format_internal.h"
>  
> -/**
> - * drm_draw_color_from_xrgb8888 - convert one pixel from xrgb8888 to the desired format
> - * @color: input color, in xrgb8888 format
> - * @format: output format
> - *
> - * Returns:
> - * Color in the format specified, casted to u32.
> - * Or 0 if the format is not supported.
> - */
> -u32 drm_draw_color_from_xrgb8888(u32 color, u32 format)
> +static int __drm_draw_color_from_xrgb8888(u32 color, u32 format, u32 *out_color)

Is there any reason to change the return value of this function and
return the result via out_color? It already returns 0 if the format is
not supported. If there's a reason, it needs to be in the commit
message.

>  {
>  	switch (format) {
>  	case DRM_FORMAT_RGB565:
> -		return drm_pixel_xrgb8888_to_rgb565(color);
> +		*out_color = drm_pixel_xrgb8888_to_rgb565(color);
> +		break;
>  	case DRM_FORMAT_RGBA5551:
> -		return drm_pixel_xrgb8888_to_rgba5551(color);
> +		*out_color = drm_pixel_xrgb8888_to_rgba5551(color);
> +		break;
>  	case DRM_FORMAT_XRGB1555:
> -		return drm_pixel_xrgb8888_to_xrgb1555(color);
> +		*out_color = drm_pixel_xrgb8888_to_xrgb1555(color);
> +		break;
>  	case DRM_FORMAT_ARGB1555:
> -		return drm_pixel_xrgb8888_to_argb1555(color);
> +		*out_color = drm_pixel_xrgb8888_to_argb1555(color);
> +		break;
>  	case DRM_FORMAT_RGB888:
> +		fallthrough;

That's not necessary for back to back case labels. Please don't add it.

>  	case DRM_FORMAT_XRGB8888:
> -		return color;
> +		*out_color = color;
> +		break;
>  	case DRM_FORMAT_ARGB8888:
> -		return drm_pixel_xrgb8888_to_argb8888(color);
> +		*out_color = drm_pixel_xrgb8888_to_argb8888(color);
> +		break;
>  	case DRM_FORMAT_XBGR8888:
> -		return drm_pixel_xrgb8888_to_xbgr8888(color);
> +		*out_color = drm_pixel_xrgb8888_to_xbgr8888(color);
> +		break;
>  	case DRM_FORMAT_ABGR8888:
> -		return drm_pixel_xrgb8888_to_abgr8888(color);
> +		*out_color = drm_pixel_xrgb8888_to_abgr8888(color);
> +		break;
>  	case DRM_FORMAT_XRGB2101010:
> -		return drm_pixel_xrgb8888_to_xrgb2101010(color);
> +		*out_color = drm_pixel_xrgb8888_to_xrgb2101010(color);
> +		break;
>  	case DRM_FORMAT_ARGB2101010:
> -		return drm_pixel_xrgb8888_to_argb2101010(color);
> +		*out_color = drm_pixel_xrgb8888_to_argb2101010(color);
> +		break;
>  	case DRM_FORMAT_ABGR2101010:
> -		return drm_pixel_xrgb8888_to_abgr2101010(color);
> +		*out_color = drm_pixel_xrgb8888_to_abgr2101010(color);
> +		break;
>  	default:
> -		WARN_ONCE(1, "Can't convert to %p4cc\n", &format);
> -		return 0;
> +		return -1;

Please don't use -1 as a generic error code. -1 is -EPERM.

>  	}
> +
> +	return 0;
> +}
> +
> +/**
> + * drm_draw_can_convert_from_xrgb8888 - check if xrgb8888 can be converted to the desired format
> + * @format: format
> + *
> + * Returns:
> + * True if XRGB8888 can be converted to the specified format, false otherwise.
> + */
> +bool drm_draw_can_convert_from_xrgb8888(u32 format)
> +{
> +	u32 out_color;
> +
> +	return __drm_draw_color_from_xrgb8888(0, format, &out_color) == 0;
> +}
> +EXPORT_SYMBOL(drm_draw_can_convert_from_xrgb8888);
> +
> +/**
> + * drm_draw_color_from_xrgb8888 - convert one pixel from xrgb8888 to the desired format
> + * @color: input color, in xrgb8888 format
> + * @format: output format
> + *
> + * Returns:
> + * Color in the format specified, casted to u32.
> + * Or 0 if the format is not supported.
> + */
> +u32 drm_draw_color_from_xrgb8888(u32 color, u32 format)
> +{
> +	u32 out_color = 0;
> +
> +	if (__drm_draw_color_from_xrgb8888(color, format, &out_color))
> +		WARN_ONCE(1, "Can't convert to %p4cc\n", &format);
> +
> +	return out_color;
>  }
>  EXPORT_SYMBOL(drm_draw_color_from_xrgb8888);
>  
> diff --git a/drivers/gpu/drm/drm_draw_internal.h b/drivers/gpu/drm/drm_draw_internal.h
> index f121ee7339dc11537f677c833f0ee94fe0e799cd..2ab4cb341df94fc4173dd6f5e7a512bdcfa5e55c 100644
> --- a/drivers/gpu/drm/drm_draw_internal.h
> +++ b/drivers/gpu/drm/drm_draw_internal.h
> @@ -24,6 +24,8 @@ static inline const u8 *drm_draw_get_char_bitmap(const struct font_desc *font,
>  	return font->data + (c * font->height) * font_pitch;
>  }
>  
> +bool drm_draw_can_convert_from_xrgb8888(u32 format);
> +
>  u32 drm_draw_color_from_xrgb8888(u32 color, u32 format);
>  
>  void drm_draw_blit16(struct iosys_map *dmap, unsigned int dpitch,

-- 
Jani Nikula, Intel