[PATCH 7/8] drm/format-helper: Optimize 32-to-16-bpp conversion

[Thomas Zimmermann]

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) {
+               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++)));
 }
-- 
2.48.1