On Tue, 25 Mar 2025, Thomas Zimmermann <tzimmerm...@suse.de> wrote:
> For ease of implementation, existing line-conversion functions
> for 16-bit formats write each pixel individually. Optimize the
> performance by writing mulitple pixels in single 64-bit and 32-bit
> stores.
>
> Signed-off-by: Thomas Zimmermann <tzimmerm...@suse.de>
> ---
> drivers/gpu/drm/drm_format_helper.c | 40 ++++++++++++++++++++++++++++-
> 1 file changed, 39 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_format_helper.c
> b/drivers/gpu/drm/drm_format_helper.c
> index b9c9c712aa9c..66137df85725 100644
> --- a/drivers/gpu/drm/drm_format_helper.c
> +++ b/drivers/gpu/drm/drm_format_helper.c
> @@ -262,10 +262,48 @@ static __always_inline void
> drm_fb_xfrm_line_32to16(void *dbuf, const void *sbuf
> unsigned int pixels,
> u32 (*xfrm_pixel)(u32))
> {
> - __le16 *dbuf16 = dbuf;
> + __le64 *dbuf64 = dbuf;
> + __le32 *dbuf32;
> + __le16 *dbuf16;
> const __le32 *sbuf32 = sbuf;
> const __le32 *send32 = sbuf32 + pixels;
>
> +#if defined(CONFIG_64BIT)
> + /* write 4 pixels at once */
> + send32 -= pixels & GENMASK(1, 0);
> + while (sbuf32 < send32) {
I find the adjusting of send32 before and after the loop with different
masks a bit confusing. Would it not suffice to:
while (sbuf32 < ALIGN_DOWN(send32, 4))
and leave send32 untouched? With different alignments for 2 pixels at a
time.
BR,
Jani.
> + u32 pix[4] = {
> + le32_to_cpup(sbuf32++),
> + le32_to_cpup(sbuf32++),
> + le32_to_cpup(sbuf32++),
> + le32_to_cpup(sbuf32++),
> + };
> + /* write output bytes in reverse order for little endianness */
> + u64 val64 = ((u64)xfrm_pixel(pix[0])) |
> + ((u64)xfrm_pixel(pix[1]) << 16) |
> + ((u64)xfrm_pixel(pix[2]) << 32) |
> + ((u64)xfrm_pixel(pix[3]) << 48);
> + *dbuf64++ = cpu_to_le64(val64);
> + }
> + send32 += pixels & GENMASK(1, 1);
> +#endif
> +
> + /* write 2 pixels at once */
> + dbuf32 = (__le32 __force *)dbuf64;
> + while (sbuf32 < send32) {
> + u32 pix[2] = {
> + le32_to_cpup(sbuf32++),
> + le32_to_cpup(sbuf32++),
> + };
> + /* write output bytes in reverse order for little endianness */
> + u32 val32 = xfrm_pixel(pix[0]) |
> + (xfrm_pixel(pix[1]) << 16);
> + *dbuf32++ = cpu_to_le32(val32);
> + }
> + send32 += pixels & GENMASK(0, 0);
> +
> + /* write trailing pixel */
> + dbuf16 = (__le16 __force *)dbuf32;
> while (sbuf32 < send32)
> *dbuf16++ = cpu_to_le16(xfrm_pixel(le32_to_cpup(sbuf32++)));
> }
--
Jani Nikula, Intel
