[1/2] drm/udl: optimize udl_compress_hline16

Commit Message

Haixia Shi Jan. 28, 2015, 9:41 p.m. UTC

The run-length encoding algorithm should compare 16-bit encoded pixel
values instead of comparing raw pixel values. It allows pixels
with similar but different colors to be encoded as repeat pixels, and
thus potentially save USB bandwidth.

Signed-off-by: Haixia Shi <[e-mail]>
Reviewed-by: Daniel Kurtz <[e-mail]>
Tested-by: Haixia Shi <[e-mail]>
---
 drivers/gpu/drm/udl/udl_transfer.c | 41 +++++++++++++++++++-------------------
 1 file changed, 20 insertions(+), 21 deletions(-)

Comments

Dave Airlie Jan. 30, 2015, 3:45 a.m. UTC | #1

On 29 January 2015 at 07:41, Haixia Shi <[e-mail]> wrote:
> The run-length encoding algorithm should compare 16-bit encoded pixel
> values instead of comparing raw pixel values. It allows pixels
> with similar but different colors to be encoded as repeat pixels, and
> thus potentially save USB bandwidth.

This fails to build here, are we missing some precursor patches?

 CC [M]  drivers/gpu/drm/udl/udl_transfer.o
/home/airlied/devel/kernel/drm-next/drivers/gpu/drm/udl/udl_transfer.c:
In function ‘get_pixel_val16’:
/home/airlied/devel/kernel/drm-next/drivers/gpu/drm/udl/udl_transfer.c:91:3:
error: implicit declaration of function ‘pixel32_to_be16p’
[-Werror=implicit-function-declaration]
   pixel_val16 = pixel32_to_be16p(pixel);
   ^
/home/airlied/devel/kernel/drm-next/drivers/gpu/drm/udl/udl_transfer.c:
In function ‘udl_compress_hline16’:
/home/airlied/devel/kernel/drm-next/drivers/gpu/drm/udl/udl_transfer.c:180:33:
error: ‘start’ undeclared (first use in this function)
     *raw_pixels_count_byte = (((start -
                                 ^
/home/airlied/devel/kernel/drm-next/drivers/gpu/drm/udl/udl_transfer.c:180:33:
note: each undeclared identifier is reported only once for each
function it appears in
cc1: some warnings being treated as errors

Dave.

Haixia Shi Jan. 30, 2015, 6:20 p.m. UTC | #2

Dave

Sorry it seems that my patch was rebased on top of
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

I'm going to re-send the patch on top of the drm-next branch of your
tree (git://people.freedesktop.org/~airlied/linux)

On Thu, Jan 29, 2015 at 7:45 PM, Dave Airlie <[e-mail]> wrote:
> On 29 January 2015 at 07:41, Haixia Shi <[e-mail]> wrote:
>> The run-length encoding algorithm should compare 16-bit encoded pixel
>> values instead of comparing raw pixel values. It allows pixels
>> with similar but different colors to be encoded as repeat pixels, and
>> thus potentially save USB bandwidth.
>
> This fails to build here, are we missing some precursor patches?
>
>  CC [M]  drivers/gpu/drm/udl/udl_transfer.o
> /home/airlied/devel/kernel/drm-next/drivers/gpu/drm/udl/udl_transfer.c:
> In function ‘get_pixel_val16’:
> /home/airlied/devel/kernel/drm-next/drivers/gpu/drm/udl/udl_transfer.c:91:3:
> error: implicit declaration of function ‘pixel32_to_be16p’
> [-Werror=implicit-function-declaration]
>    pixel_val16 = pixel32_to_be16p(pixel);
>    ^
> /home/airlied/devel/kernel/drm-next/drivers/gpu/drm/udl/udl_transfer.c:
> In function ‘udl_compress_hline16’:
> /home/airlied/devel/kernel/drm-next/drivers/gpu/drm/udl/udl_transfer.c:180:33:
> error: ‘start’ undeclared (first use in this function)
>      *raw_pixels_count_byte = (((start -
>                                  ^
> /home/airlied/devel/kernel/drm-next/drivers/gpu/drm/udl/udl_transfer.c:180:33:
> note: each undeclared identifier is reported only once for each
> function it appears in
> cc1: some warnings being treated as errors
>
> Dave.

Patch

diff --git a/drivers/gpu/drm/udl/udl_transfer.c b/drivers/gpu/drm/udl/udl_transfer.c
index f343db7..eadddf9 100644
--- a/drivers/gpu/drm/udl/udl_transfer.c
+++ b/drivers/gpu/drm/udl/udl_transfer.c
@@ -82,12 +82,14 @@  static inline u16 pixel32_to_be16(const uint32_t pixel)
 		((pixel >> 8) & 0xf800));
 }
 
-static bool pixel_repeats(const void *pixel, const uint32_t repeat, int bpp)
+static inline u16 get_pixel_val16(const uint8_t *pixel, int bpp)
 {
+	u16 pixel_val16 = 0;
 	if (bpp == 2)
-		return *(const uint16_t *)pixel == repeat;
-	else
-		return *(const uint32_t *)pixel == repeat;
+		pixel_val16 = *(uint16_t *)pixel;
+	else if (bpp == 4)
+		pixel_val16 = pixel32_to_be16p(pixel);
+	return pixel_val16;
 }
 
 /*
@@ -134,6 +136,7 @@  static void udl_compress_hline16(
 		uint8_t *cmd_pixels_count_byte = NULL;
 		const u8 *raw_pixel_start = NULL;
 		const u8 *cmd_pixel_start, *cmd_pixel_end = NULL;
+		uint16_t pixel_val16;
 
 		prefetchw((void *) cmd); /* pull in one cache line at least */
 
@@ -154,33 +157,29 @@  static void udl_compress_hline16(
 			    (int)(cmd_buffer_end - cmd) / 2))) * bpp;
 
 		prefetch_range((void *) pixel, (cmd_pixel_end - pixel) * bpp);
+		pixel_val16 = get_pixel_val16(pixel, bpp);
 
 		while (pixel < cmd_pixel_end) {
-			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));
-			}
+			const u8 * const repeating_pixel = pixel;
+			const uint16_t repeating_pixel_val16 = pixel_val16;
+
+			*(uint16_t *)cmd = cpu_to_be16(pixel_val16);
 
 			cmd += 2;
 			pixel += bpp;
 
-			if (unlikely((pixel < cmd_pixel_end) &&
-				     (pixel_repeats(pixel, repeating_pixel, bpp)))) {
+			while (pixel < cmd_pixel_end) {
+				pixel_val16 = get_pixel_val16(pixel, bpp);
+				if (pixel_val16 != repeating_pixel_val16)
+					break;
+				pixel += bpp;
+			}
+
+			if (unlikely(pixel > repeating_pixel + bpp)) {
 				/* go back and fill in raw pixel count */
 				*raw_pixels_count_byte = (((start -
 						raw_pixel_start) / bpp) + 1) & 0xFF;
 
-				while ((pixel < cmd_pixel_end) &&
-				       (pixel_repeats(pixel, repeating_pixel, bpp))) {
-					pixel += bpp;
-				}
-
 				/* immediately after raw data is repeat byte */
 				*cmd++ = (((pixel - start) / bpp) - 1) & 0xFF;