[PATCH] fbdev: fix CVT vertical front and back porch values

-----Original Message-----
From: Tomi Valkeinen [mailto:tomi.valkeinen@ti.com]
Sent: Monday, January 26, 2015 5:11 AM
To: linux-fbdev@vger.kernel.org
Cc: Tomi Valkeinen; David Ung; Antonino A. Daplas
Subject: [PATCH] fbdev: fix CVT vertical front and back porch values

CVT v1.1 spec says: "the vertical front porch shall in all cases be fixed to 3
lines". The code in fbcvt.c instead sets the _back_ porch to
3 (plus margin).

After swapping cvt.v_front_porch and cvt.v_back_porch the resulting
timings were in line with CVT timings in VESA DMT spec.

The bug seems to be more than 9 years old, but I presume it has not been
noticed as usually the video timings come from the EDID or from the timing
tables in fbdev, and probably swapped values for vfp and vbp work fine for
most of the displays.

Signed-off-by: Tomi Valkeinen <redacted>
Cc: David Ung <redacted>
Cc: Antonino A. Daplas <adaplas@gmail.com>
---
 drivers/video/fbdev/core/fbcvt.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbdev/core/fbcvt.c

b/drivers/video/fbdev/core/fbcvt.c
index 7cb715dfc0e1..55d2bd0ce5c0 100644

--- a/drivers/video/fbdev/core/fbcvt.c
+++ b/drivers/video/fbdev/core/fbcvt.c

@@ -369,9 +369,9 @@ int fb_find_mode_cvt(struct fb_videomode *mode,

int margins, int rb)
 	cvt.h_back_porch = cvt.hblank/2 + cvt.h_margin;
 	cvt.h_front_porch = cvt.hblank - cvt.hsync - cvt.h_back_porch +
 		2 * cvt.h_margin;
-	cvt.v_back_porch = 3 + cvt.v_margin;
-	cvt.v_front_porch = cvt.vtotal - cvt.yres/cvt.interlace -
-	    cvt.v_back_porch - cvt.vsync;
+	cvt.v_front_porch = 3 + cvt.v_margin;
+	cvt.v_back_porch = cvt.vtotal - cvt.yres/cvt.interlace -
+	    cvt.v_front_porch - cvt.vsync;
 	fb_cvt_print_name(&cvt);
 	fb_cvt_convert_to_mode(&cvt, mode);

--
2.2.2