This is a note to let you know that I've just added the patch titled
drm/i915/pch: Fix integer math bugs in panel fitting
to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-i915-pch-fix-integer-math-bugs-in-panel-fitting.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <sta...@kernel.org> know about it.
>From 302983e9059e9ef5de3ca7671918eeb237c5971e Mon Sep 17 00:00:00 2001
From: Adam Jackson <a...@redhat.com>
Date: Wed, 13 Jul 2011 16:32:32 -0400
Subject: drm/i915/pch: Fix integer math bugs in panel fitting
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From: Adam Jackson <a...@redhat.com>
commit 302983e9059e9ef5de3ca7671918eeb237c5971e upstream.
Consider a 1600x900 panel, upscaling a 1360x768 mode, full-aspect. The
old math would give you:
scaled_width = 1600 * 768; /* 1228800 */
scaled_height = 1360 * 900; /* 1224000 */
if (scaled_width > scaled_height) { /* pillarbox, and true */
width = 1224000 / 768; /* int(1593.75) = 1593 */
x = (1600 - 1593 + 1) / 2; /* 4 */
y = 0;
height = 768;
} /* ... */
This is broken. The total width of scanout would then be 1593 + 4 + 4,
or 1601, which is wider than the panel itself. The hardware very
dutifully implements this, and you end up with a black 45° diagonal from
the top-left corner to the bottom edge of the screen. It's a cool
effect and all, but not what you wanted. Similar things happen for the
letterbox case.
The problem is that you have an integer number of pixels, which means
it's usually impossible to upscale equally on both axes. 1360/768 is
1.7708, 1600/900 is 1.7777. Since we're constrained on the one axis,
the other one wants to come out as an even number of pixels (the panel
is almost certainly even on both axes, and the x/y offsets will be
applied on both sides). In the math above, if 'width' comes out even,
rounding down is correct; if it's odd, you'd rather round up. So just
increment width/height in those cases.
Tested on a Lenovo T500 (Ironlake).
Signed-off-by: Adam Jackson <a...@redhat.com>
Tested-By: Daniel Manrique <daniel.manri...@canonical.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38851
Reviewed-by: Chris Wilson <ch...@chris-wilson.co.uk>
Signed-off-by: Keith Packard <kei...@keithp.com>
Signed-off-by: Greg Kroah-Hartman <gre...@suse.de>
---
drivers/gpu/drm/i915/intel_panel.c | 4 ++++
1 file changed, 4 insertions(+)
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -83,11 +83,15 @@ intel_pch_panel_fitting(struct drm_devic
u32 scaled_height = mode->hdisplay *
adjusted_mode->vdisplay;
if (scaled_width > scaled_height) { /* pillar */
width = scaled_height / mode->vdisplay;
+ if (width & 1)
+ width++;
x = (adjusted_mode->hdisplay - width + 1) / 2;
y = 0;
height = adjusted_mode->vdisplay;
} else if (scaled_width < scaled_height) { /* letter */
height = scaled_width / mode->hdisplay;
+ if (height & 1)
+ height++;
y = (adjusted_mode->vdisplay - height + 1) / 2;
x = 0;
width = adjusted_mode->hdisplay;
Patches currently in stable-queue which might be from a...@redhat.com are
queue-3.0/drm-i915-pch-fix-integer-math-bugs-in-panel-fitting.patch
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