Re: [PATCH] fbdev: fix parsing of standard timings

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

Hi Florian,

On Fri, 2011-08-26 at 18:02 +0000, Florian Tobias Schandinat wrote:
> Hi Tomi,
> 
> On 08/26/2011 12:38 PM, Tomi Valkeinen wrote:
> > The standard timings parses uses 1:1 dimensions when the ratio in the
> > EDID data is 0. However, for EDID 1.3 and later the dimensions are 16:10
> > when the ratio is 0.
> > 
> > Pass the version and revision numbers to get_std_timing() which can then
> > make the right decision about dimensions.
> > 
> > Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
> 
> Thanks, looks good to me.
> I'd be happy if someone with access to the original EDID specs could confirm
> this and add his reviewed by.
> I also think adding a comment explaining this change would be helpful.

You can see the same thing done in
drivers/gpu/drm/drm_edid.c:drm_mode_std(). Although they seem to check
only revision, which looks a bit risky to me.

The specs seem to be available by just googling them, although I don't
know if it's legal to distribute them or not...

I've added your comment, I agree it's good. Patch below.

 Tomi


From 82c630291ad39d45009352fce1b23b4d0f44f92d Mon Sep 17 00:00:00 2001
From: Tomi Valkeinen <tomi.valkeinen@ti.com>
Date: Thu, 25 Aug 2011 15:36:40 +0300
Subject: [PATCH] fbdev: fix parsing of standard timings

The standard timings parses uses 1:1 dimensions when the ratio in the
EDID data is 0. However, for EDID 1.3 and later the dimensions are 16:10
when the ratio is 0.

Pass the version and revision numbers to get_std_timing() which can then
make the right decision about dimensions.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
---
 drivers/video/fbmon.c |   21 +++++++++++++++------
 1 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/drivers/video/fbmon.c b/drivers/video/fbmon.c
index 4f57485..cef6557 100644
--- a/drivers/video/fbmon.c
+++ b/drivers/video/fbmon.c
@@ -493,7 +493,8 @@ static int get_est_timing(unsigned char *block, struct fb_videomode *mode)
 	return num;
 }
 
-static int get_std_timing(unsigned char *block, struct fb_videomode *mode)
+static int get_std_timing(unsigned char *block, struct fb_videomode *mode,
+		int ver, int rev)
 {
 	int xres, yres = 0, refresh, ratio, i;
 
@@ -504,7 +505,11 @@ static int get_std_timing(unsigned char *block, struct fb_videomode *mode)
 	ratio = (block[1] & 0xc0) >> 6;
 	switch (ratio) {
 	case 0:
-		yres = xres;
+		/* in EDID 1.3 the meaning of 0 changed to 16:10 (prior 1:1) */
+		if (ver < 1 || (ver = 1 && rev < 3))
+			yres = xres;
+		else
+			yres = (xres * 10)/16;
 		break;
 	case 1:
 		yres = (xres * 3)/4;
@@ -533,12 +538,12 @@ static int get_std_timing(unsigned char *block, struct fb_videomode *mode)
 }
 
 static int get_dst_timing(unsigned char *block,
-			  struct fb_videomode *mode)
+			  struct fb_videomode *mode, int ver, int rev)
 {
 	int j, num = 0;
 
 	for (j = 0; j < 6; j++, block += STD_TIMING_DESCRIPTION_SIZE)
-		num += get_std_timing(block, &mode[num]);
+		num += get_std_timing(block, &mode[num], ver, rev);
 
 	return num;
 }
@@ -599,6 +604,10 @@ static struct fb_videomode *fb_create_modedb(unsigned char *edid, int *dbsize)
 	struct fb_videomode *mode, *m;
 	unsigned char *block;
 	int num = 0, i, first = 1;
+	int ver, rev;
+
+	ver = edid[EDID_STRUCT_VERSION];
+	rev = edid[EDID_STRUCT_REVISION];
 
 	mode = kzalloc(50 * sizeof(struct fb_videomode), GFP_KERNEL);
 	if (mode = NULL)
@@ -632,12 +641,12 @@ static struct fb_videomode *fb_create_modedb(unsigned char *edid, int *dbsize)
 	DPRINTK("   Standard Timings\n");
 	block = edid + STD_TIMING_DESCRIPTIONS_START;
 	for (i = 0; i < STD_TIMING; i++, block += STD_TIMING_DESCRIPTION_SIZE)
-		num += get_std_timing(block, &mode[num]);
+		num += get_std_timing(block, &mode[num], ver, rev);
 
 	block = edid + DETAILED_TIMING_DESCRIPTIONS_START;
 	for (i = 0; i < 4; i++, block+= DETAILED_TIMING_DESCRIPTION_SIZE) {
 		if (block[0] = 0x00 && block[1] = 0x00 && block[3] = 0xfa)
-			num += get_dst_timing(block + 5, &mode[num]);
+			num += get_dst_timing(block + 5, &mode[num], ver, rev);
 	}
 
 	/* Yikes, EDID data is totally useless */
-- 
1.7.4.1