drm/udl: Inline memcmp() for RLE compression of xfer

As we use a variable length the compiler does not realise that it is a
fixed value of either 2 or 4 bytes. Instead of performing the inline
comparison itself, the compiler inserts a function call to the generic
memcmp routine which is optimised for long comparisons of variable
length. That turns out to be quite expensive...

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 28 insertions, 18 deletions

diff --git a/drivers/gpu/drm/udl/udl_transfer.c b/drivers/gpu/drm/udl/udl_transfer.c
index 142fee5f983f..f343db73e095 100644
--- a/drivers/gpu/drm/udl/udl_transfer.c
+++ b/drivers/gpu/drm/udl/udl_transfer.c
@@ -75,15 +75,19 @@ static int udl_trim_hline(const u8 *bback, const u8 **bfront, int *width_bytes)
 }
 #endif
 
-static inline u16 pixel32_to_be16p(const uint8_t *pixel)
+static inline u16 pixel32_to_be16(const uint32_t pixel)
 {
-        uint32_t pix = *(uint32_t *)pixel;
-        u16 retval;
+        return (((pixel >> 3) & 0x001f) |
+                ((pixel >> 5) & 0x07e0) |
+                ((pixel >> 8) & 0xf800));
+}
 
-        retval =  (((pix >> 3) & 0x001f) |
-                   ((pix >> 5) & 0x07e0) |
-                   ((pix >> 8) & 0xf800));
-        return retval;
+static bool pixel_repeats(const void *pixel, const uint32_t repeat, int bpp)
+{
+        if (bpp == 2)
+                return *(const uint16_t *)pixel == repeat;
+        else
+                return *(const uint32_t *)pixel == repeat;
 }
 
 /*
@@ -152,29 +156,33 @@ static void udl_compress_hline16(
                 prefetch_range((void *) pixel, (cmd_pixel_end - pixel) * bpp);
 
                 while (pixel < cmd_pixel_end) {
-                        const u8 * const repeating_pixel = pixel;
-
-                        if (bpp == 2)
-                                *(uint16_t *)cmd = cpu_to_be16p((uint16_t *)pixel);
-                        else if (bpp == 4)
-                                *(uint16_t *)cmd = cpu_to_be16(pixel32_to_be16p(pixel));
+                        const u8 *const start = pixel;
+                        u32 repeating_pixel;
+
+                        if (bpp == 2) {
+                                repeating_pixel = *(uint16_t *)pixel;
+                                *(uint16_t *)cmd = cpu_to_be16(repeating_pixel);
+                        } else {
+                                repeating_pixel = *(uint32_t *)pixel;
+                                *(uint16_t *)cmd = cpu_to_be16(pixel32_to_be16(repeating_pixel));
+                        }
 
                         cmd += 2;
                         pixel += bpp;
 
                         if (unlikely((pixel < cmd_pixel_end) &&
-                                     (!memcmp(pixel, repeating_pixel, bpp)))) {
+                                     (pixel_repeats(pixel, repeating_pixel, bpp)))) {
                                 /* go back and fill in raw pixel count */
-                                *raw_pixels_count_byte = (((repeating_pixel -
+                                *raw_pixels_count_byte = (((start -
                                                 raw_pixel_start) / bpp) + 1) & 0xFF;
 
-                                while ((pixel < cmd_pixel_end)
-                                       && (!memcmp(pixel, repeating_pixel, bpp))) {
+                                while ((pixel < cmd_pixel_end) &&
+                                       (pixel_repeats(pixel, repeating_pixel, bpp))) {
                                         pixel += bpp;
                                 }
 
                                 /* immediately after raw data is repeat byte */
-                                *cmd++ = (((pixel - repeating_pixel) / bpp) - 1) & 0xFF;
+                                *cmd++ = (((pixel - start) / bpp) - 1) & 0xFF;
 
                                 /* Then start another raw pixel span */
                                 raw_pixel_start = pixel;
@@ -223,6 +231,8 @@ int udl_render_hline(struct drm_device *dev, int bpp, struct urb **urb_ptr,
         u8 *cmd = *urb_buf_ptr;
         u8 *cmd_end = (u8 *) urb->transfer_buffer + urb->transfer_buffer_length;
 
+        BUG_ON(!(bpp == 2 || bpp == 4));
+
         line_start = (u8 *) (front + byte_offset);
         next_pixel = line_start;
         line_end = next_pixel + byte_width;