On Wed, 2011-07-13 at 16:32 -0400, Adam Jackson wrote:
> 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 <[email protected]>
> ---
> drivers/gpu/drm/i915/intel_panel.c | 4 ++++
> 1 files changed, 4 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_panel.c
> b/drivers/gpu/drm/i915/intel_panel.c
> index a06ff07..05f500c 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;We've seen this in Ubuntu in the form of https://bugs.launchpad.net/ubuntu/+source/linux/+bug/753994 so we can add a Tested-By: Daniel Manrique <[email protected]>
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