From 715245b55733d3a3ca1f336dd0682f83836c7625 Mon Sep 17 00:00:00 2001 From: Adam Jackson Date: Wed, 13 Jul 2011 16:32:32 -0400 Subject: drm/i915/pch: Fix integer math bugs in panel fitting MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Tested-By: Daniel Manrique Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38851 Reviewed-by: Chris Wilson Signed-off-by: Keith Packard Signed-off-by: Greg Kroah-Hartman --- drivers/gpu/drm/i915/intel_panel.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'drivers/gpu') diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c index a06ff07a4d3..05f500cd9c2 100644 --- 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_device *dev, 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; -- cgit v1.2.3