drm/format-helper: Optimize 32-to-16-bpp conversion

For ease of implementation, existing line-conversion functions
for 16-bit formats write each pixel individually. Optimize the
performance by writing multiple pixels in single 64-bit and 32-bit
stores.

v2:
- simplify address calculation (Jani)
- fix typo in commit message (Jocelyn)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://lore.kernel.org/r/20250328141709.217283-8-tzimmermann@suse.de

diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
index daf5a6d4f28355abbef0c8cf574c943ae2c31bc5..5098a00803d230f28acc4f18d97301a3fc69def9 100644 (file)
--- a/drivers/gpu/drm/drm_format_helper.c
+++ b/drivers/gpu/drm/drm_format_helper.c
@@ -265,10 +265,45 @@ 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 */
+       while (sbuf32 < ALIGN_DOWN_PIXELS(send32, pixels, 4)) {
+               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);
+       }
+#endif
+
+       /* write 2 pixels at once */
+       dbuf32 = (__le32 __force *)dbuf64;
+       while (sbuf32 < ALIGN_DOWN_PIXELS(send32, pixels, 2)) {
+               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);
+       }
+
+       /* write trailing pixel */
+       dbuf16 = (__le16 __force *)dbuf32;
        while (sbuf32 < send32)
                *dbuf16++ = cpu_to_le16(xfrm_pixel(le32_to_cpup(sbuf32++)));
 }