[PATCH 6/8] drm/format-helper: Optimize 32-to-24-bpp conversion

[Jocelyn Falempe]

On 25/03/2025 11:31, Thomas Zimmermann wrote:
> For ease of implementation, existing line-conversion functions
> for 24-bit formats write each byte individually. Optimize the
> performance by writing 4 pixels in 3 32-bit stores.
> 
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 | 36 ++++++++++++++++++++++++++++-
>   1 file changed, 35 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
> index a926aa6671fc..b9c9c712aa9c 100644
> --- a/drivers/gpu/drm/drm_format_helper.c
> +++ b/drivers/gpu/drm/drm_format_helper.c
> @@ -274,10 +274,44 @@ static __always_inline void drm_fb_xfrm_line_32to24(void *dbuf, const void *sbuf
>   						    unsigned int pixels,
>   						    u32 (*xfrm_pixel)(u32))
>   {
> -	u8 *dbuf8 = dbuf;
> +	__le32 *dbuf32 = dbuf;
> +	u8 *dbuf8;
>   	const __le32 *sbuf32 = sbuf;
>   	const __le32 *send32 = sbuf32 + pixels;
>   
> +	/* write pixels in chunks of 4 */
> +	send32 -= pixels & GENMASK(1, 0);
> +	while (sbuf32 < send32) {
> +		u32 val24[4] = {
> +			xfrm_pixel(le32_to_cpup(sbuf32++)),
> +			xfrm_pixel(le32_to_cpup(sbuf32++)),
> +			xfrm_pixel(le32_to_cpup(sbuf32++)),
> +			xfrm_pixel(le32_to_cpup(sbuf32++)),
> +		};
> +		u32 out32[3] = {
> +			/* write output bytes in reverse order for little endianness */
> +			((val24[0] & 0x000000ff)) |
> +			((val24[0] & 0x0000ff00)) |
> +			((val24[0] & 0x00ff0000)) |
> +			((val24[1] & 0x000000ff) << 24),
> +			((val24[1] & 0x0000ff00) >> 8) |
> +			((val24[1] & 0x00ff0000) >> 8) |
> +			((val24[2] & 0x000000ff) << 16) |
> +			((val24[2] & 0x0000ff00) << 16),
> +			((val24[2] & 0x00ff0000) >> 16) |
> +			((val24[3] & 0x000000ff) << 8) |
> +			((val24[3] & 0x0000ff00) << 8) |
> +			((val24[3] & 0x00ff0000) << 8),
> +		};
> +
> +		*dbuf32++ = cpu_to_le32(out32[0]);
> +		*dbuf32++ = cpu_to_le32(out32[1]);
> +		*dbuf32++ = cpu_to_le32(out32[2]);
> +	}
> +	send32 += pixels & GENMASK(1, 0);
> +
> +	/* write trailing pixel */
> +	dbuf8 = (u8 __force *)dbuf32;
>   	while (sbuf32 < send32) {
>   		u32 val24 = xfrm_pixel(le32_to_cpup(sbuf32++));
>   		/* write output in reverse order for little endianness */