frombugzilla-dae...@freedesktop.org toj.mag.guth...@gmail.com dateFri, Jul 29, 2011 at 4:04 AMsubject[Bug 38851] 1360x768 resolution slants/wraps-around display in kernels newer than 2.6.32mailed-by freedesktop.orgImportant mainly because of your interaction with messages in the conversation. hide details 4:04 AM (5 hours ago)
https://bugs.freedesktop.org/show_bug.cgi?id=38851 Chris Wilson <ch...@chris-wilson.co.uk> changed: What |Removed |Added ------------------------------ ---------------------------------------------- Status|NEW |RESOLVED Resolution| |FIXED --- Comment #7 from Chris Wilson <ch...@chris-wilson.co.uk> 2011-07-29 02:04:34 PDT --- I was waiting upon the attachments bugzilla kept stripping. Fortunately Adam Jackson found the bug, and in drm-intel-fixes: commit 302983e9059e9ef5de3ca7671918eeb237c5971e Author: Adam Jackson <a...@redhat.com> Date: Wed Jul 13 16:32:32 2011 -0400 drm/i915/pch: Fix integer math bugs in panel fitting 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> Cc: sta...@kernel.org Signed-off-by: Keith Packard <kei...@keithp.com>