[PATCH 3/8] drm/format-helper: Add generic conversion to 24-bit formats

[Jocelyn Falempe]

On 25/03/2025 11:31, Thomas Zimmermann wrote:
> Add drm_fb_xfrm_line_32to24() to implement conversion from 32-bit
> pixels to 24-bit pixels. The pixel-conversion is specified by the
> given callback parameter. Mark the helper as always_inline to avoid
> overhead from function calls.
> 
> Then implement all existing line-conversion functions with the new
> generic call and the respective pixel-conversion helper.

Thanks, it looks good to me.

Reviewed-by: Jocelyn Falempe <jfalempe at redhat.com>

> 
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> ---
>   drivers/gpu/drm/drm_format_helper.c   | 43 ++++++++++++---------------
>   drivers/gpu/drm/drm_format_internal.h | 12 ++++++++
>   2 files changed, 31 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
> index abd18c23cfbb..5a2fe3d685a2 100644
> --- a/drivers/gpu/drm/drm_format_helper.c
> +++ b/drivers/gpu/drm/drm_format_helper.c
> @@ -246,6 +246,23 @@ static int drm_fb_xfrm(struct iosys_map *dst,
>   				     xfrm_line);
>   }
>   
> +static __always_inline void drm_fb_xfrm_line_32to24(void *dbuf, const void *sbuf,
> +						    unsigned int pixels,
> +						    u32 (*xfrm_pixel)(u32))
> +{
> +	u8 *dbuf8 = dbuf;
> +	const __le32 *sbuf32 = sbuf;
> +	const __le32 *send32 = sbuf32 + pixels;
> +
> +	while (sbuf32 < send32) {
> +		u32 val24 = xfrm_pixel(le32_to_cpup(sbuf32++));
> +		/* write output in reverse order for little endianness */
> +		*dbuf8++ = (val24 & 0x000000ff);
> +		*dbuf8++ = (val24 & 0x0000ff00) >>  8;
> +		*dbuf8++ = (val24 & 0x00ff0000) >> 16;
> +	}
> +}
> +
>   static __always_inline void drm_fb_xfrm_line_32to32(void *dbuf, const void *sbuf,
>   						    unsigned int pixels,
>   						    u32 (*xfrm_pixel)(u32))
> @@ -667,18 +684,7 @@ EXPORT_SYMBOL(drm_fb_xrgb8888_to_rgba5551);
>   
>   static void drm_fb_xrgb8888_to_rgb888_line(void *dbuf, const void *sbuf, unsigned int pixels)
>   {
> -	u8 *dbuf8 = dbuf;
> -	const __le32 *sbuf32 = sbuf;
> -	unsigned int x;
> -	u32 pix;
> -
> -	for (x = 0; x < pixels; x++) {
> -		pix = le32_to_cpu(sbuf32[x]);
> -		/* write blue-green-red to output in little endianness */
> -		*dbuf8++ = (pix & 0x000000FF) >>  0;
> -		*dbuf8++ = (pix & 0x0000FF00) >>  8;
> -		*dbuf8++ = (pix & 0x00FF0000) >> 16;
> -	}
> +	drm_fb_xfrm_line_32to24(dbuf, sbuf, pixels, drm_pixel_xrgb8888_to_rgb888);
>   }
>   
>   /**
> @@ -718,18 +724,7 @@ EXPORT_SYMBOL(drm_fb_xrgb8888_to_rgb888);
>   
>   static void drm_fb_xrgb8888_to_bgr888_line(void *dbuf, const void *sbuf, unsigned int pixels)
>   {
> -	u8 *dbuf8 = dbuf;
> -	const __le32 *sbuf32 = sbuf;
> -	unsigned int x;
> -	u32 pix;
> -
> -	for (x = 0; x < pixels; x++) {
> -		pix = le32_to_cpu(sbuf32[x]);
> -		/* write red-green-blue to output in little endianness */
> -		*dbuf8++ = (pix & 0x00ff0000) >> 16;
> -		*dbuf8++ = (pix & 0x0000ff00) >> 8;
> -		*dbuf8++ = (pix & 0x000000ff) >> 0;
> -	}
> +	drm_fb_xfrm_line_32to24(dbuf, sbuf, pixels, drm_pixel_xrgb8888_to_bgr888);
>   }
>   
>   /**
> diff --git a/drivers/gpu/drm/drm_format_internal.h b/drivers/gpu/drm/drm_format_internal.h
> index 5f82f0b9c8e8..e7fcf260a914 100644
> --- a/drivers/gpu/drm/drm_format_internal.h
> +++ b/drivers/gpu/drm/drm_format_internal.h
> @@ -68,6 +68,18 @@ static inline u32 drm_pixel_xrgb8888_to_argb1555(u32 pix)
>   	       drm_pixel_xrgb8888_to_xrgb1555(pix);
>   }
>   
> +static inline u32 drm_pixel_xrgb8888_to_rgb888(u32 pix)
> +{
> +	return pix & GENMASK(23, 0);
> +}
> +
> +static inline u32 drm_pixel_xrgb8888_to_bgr888(u32 pix)
> +{
> +	return ((pix & 0x00ff0000) >> 16) |
> +	       ((pix & 0x0000ff00)) |
> +	       ((pix & 0x000000ff) << 16);
> +}
> +
>   static inline u32 drm_pixel_xrgb8888_to_argb8888(u32 pix)
>   {
>   	return GENMASK(31, 24) | /* fill alpha bits */