[PATCH 5/8] drm/format-helper: Add generic conversion to 8-bit formats

[Jocelyn Falempe]

On 25/03/2025 11:31, Thomas Zimmermann wrote:
> Add drm_fb_xfrm_line_32to8() to implement conversion from 32-bit
> pixels to 8-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   | 38 ++++++++++-----------------
>   drivers/gpu/drm/drm_format_internal.h | 17 ++++++++++++
>   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 aecf55c1fc6b..a926aa6671fc 100644
> --- a/drivers/gpu/drm/drm_format_helper.c
> +++ b/drivers/gpu/drm/drm_format_helper.c
> @@ -246,6 +246,18 @@ static int drm_fb_xfrm(struct iosys_map *dst,
>   				     xfrm_line);
>   }
>   
> +static __always_inline void drm_fb_xfrm_line_32to8(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)
> +		*dbuf8++ = xfrm_pixel(le32_to_cpup(sbuf32++));
> +}
> +
>   static __always_inline void drm_fb_xfrm_line_32to16(void *dbuf, const void *sbuf,
>   						    unsigned int pixels,
>   						    u32 (*xfrm_pixel)(u32))
> @@ -411,17 +423,7 @@ EXPORT_SYMBOL(drm_fb_swab);
>   
>   static void drm_fb_xrgb8888_to_rgb332_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]);
> -		dbuf8[x] = ((pix & 0x00e00000) >> 16) |
> -			   ((pix & 0x0000e000) >> 11) |
> -			   ((pix & 0x000000c0) >> 6);
> -	}
> +	drm_fb_xfrm_line_32to8(dbuf, sbuf, pixels, drm_pixel_xrgb8888_to_rgb332);
>   }
>   
>   /**
> @@ -879,19 +881,7 @@ EXPORT_SYMBOL(drm_fb_xrgb8888_to_argb2101010);
>   
>   static void drm_fb_xrgb8888_to_gray8_line(void *dbuf, const void *sbuf, unsigned int pixels)
>   {
> -	u8 *dbuf8 = dbuf;
> -	const __le32 *sbuf32 = sbuf;
> -	unsigned int x;
> -
> -	for (x = 0; x < pixels; x++) {
> -		u32 pix = le32_to_cpu(sbuf32[x]);
> -		u8 r = (pix & 0x00ff0000) >> 16;
> -		u8 g = (pix & 0x0000ff00) >> 8;
> -		u8 b =  pix & 0x000000ff;
> -
> -		/* ITU BT.601: Y = 0.299 R + 0.587 G + 0.114 B */
> -		*dbuf8++ = (3 * r + 6 * g + b) / 10;
> -	}
> +	drm_fb_xfrm_line_32to8(dbuf, sbuf, pixels, drm_pixel_xrgb8888_to_r8_bt601);
>   }
>   
>   /**
> diff --git a/drivers/gpu/drm/drm_format_internal.h b/drivers/gpu/drm/drm_format_internal.h
> index 4f20b63cb6f6..9f857bfa368d 100644
> --- a/drivers/gpu/drm/drm_format_internal.h
> +++ b/drivers/gpu/drm/drm_format_internal.h
> @@ -35,6 +35,23 @@
>    * Conversions from XRGB8888
>    */
>   
> +static inline u32 drm_pixel_xrgb8888_to_r8_bt601(u32 pix)
> +{
> +	u32 r = (pix & 0x00ff0000) >> 16;
> +	u32 g = (pix & 0x0000ff00) >> 8;
> +	u32 b =  pix & 0x000000ff;
> +
> +	/* ITU-R BT.601: Y = 0.299 R + 0.587 G + 0.114 B */
> +	return (3 * r + 6 * g + b) / 10;
> +}
> +
> +static inline u32 drm_pixel_xrgb8888_to_rgb332(u32 pix)
> +{
> +	return ((pix & 0x00e00000) >> 16) |
> +	       ((pix & 0x0000e000) >> 11) |
> +	       ((pix & 0x000000c0) >> 6);
> +}
> +
>   static inline u32 drm_pixel_xrgb8888_to_rgb565(u32 pix)
>   {
>   	return ((pix & 0x00f80000) >> 8) |