fbsplash: support non-RGB565 pixels in 16-bit mode

function                                             old     new   delta
fbsplash_main                                        953     989     +36
fb_pixel_value                                        80     110     +30

Signed-off-by: Linus Walleij <triad@df.lth.se>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 22 insertions, 5 deletions

diff --git a/miscutils/fbsplash.c b/miscutils/fbsplash.c
index 988439b..37ca665 100644
--- a/miscutils/fbsplash.c
+++ b/miscutils/fbsplash.c
@@ -50,6 +50,10 @@ struct globals {
 	struct fb_var_screeninfo scr_var;
 	struct fb_fix_screeninfo scr_fix;
 	unsigned bytes_per_pixel;
+	// cached (8 - scr_var.COLOR.length):
+	unsigned red_shift;
+	unsigned green_shift;
+	unsigned blue_shift;
 };
 #define G (*ptr_to_globals)
 #define INIT_G() do { \
@@ -139,6 +143,9 @@ static void fb_open(const char *strfb_device)
 		break;
 	}
 
+	G.red_shift   = 8 - G.scr_var.red.length;
+	G.green_shift = 8 - G.scr_var.green.length;
+	G.blue_shift  = 8 - G.scr_var.blue.length;
 	G.bytes_per_pixel = (G.scr_var.bits_per_pixel + 7) >> 3;
 
 	// map the device in memory
@@ -155,10 +162,13 @@ static void fb_open(const char *strfb_device)
 
 
 /**
- * Return pixel value of the passed RGB color
+ * Return pixel value of the passed RGB color.
+ * This is performance critical fn.
  */
 static unsigned fb_pixel_value(unsigned r, unsigned g, unsigned b)
 {
+	/* We assume that the r,g,b values are <= 255 */
+
 	if (G.bytes_per_pixel == 1) {
 		r = r        & 0xe0; // 3-bit red
 		g = (g >> 3) & 0x1c; // 3-bit green
@@ -166,10 +176,17 @@ static unsigned fb_pixel_value(unsigned r, unsigned g, unsigned b)
 		return r + g + b;
 	}
 	if (G.bytes_per_pixel == 2) {
-		r = (r & 0xf8) << 8; // 5-bit red
-		g = (g & 0xfc) << 3; // 6-bit green
-		b =  b >> 3;         // 5-bit blue
-		return r + g + b;
+		// ARM PL110 on Integrator/CP has RGBA5551 bit arrangement.
+		// We want to support bit locations like that.
+		//
+		// First shift out unused bits
+		r = r >> G.red_shift;
+		g = g >> G.green_shift;
+		b = b >> G.blue_shift;
+		// Then shift the remaining bits to their offset
+		return (r << G.scr_var.red.offset) +
+			(g << G.scr_var.green.offset) +
+			(b << G.scr_var.blue.offset);
 	}
 	// RGB 888
 	return b + (g << 8) + (r << 16);