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: NAdam Jackson <ajax@redhat.com>
Tested-By: NDaniel Manrique <daniel.manrique@canonical.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38851Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org
Signed-off-by: NKeith Packard <keithp@keithp.com>

At least on my HP 2540p this is wrong at bootup, fine
at any other time once a lid event has occured. This is due to
_REG vs _INI ordering in the ACPI tables.
Signed-off-by: NDave Airlie <airlied@redhat.com>

This reverts commit 951f3512

    drm/i915: Do not handle backlight combination mode specially

since this commit introduced other regressions due to untouched LBPC
register, e.g. the backlight dimmed after resume.

In addition to the revert, this patch includes a fix for the original
issue (weird backlight levels) by removing the wrong bit shift for
computing the current backlight level.
Also, including typo fixes (lpbc -> lbpc).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=34524Acked-by: NIndan Zupancic <indan@nul.nu>
Reviewed-by: NKeith Packard <keithp@keithp.com>
Reviewed-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Cc: <stable@kernel.org>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Seems like we are forever to be cursed with buggy firmware, so allow the
user to explicitly set the panel connection status.

Of secondary utility for cases where I run laptops with the lid closed,
but still want to configure the LVDS.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>

The current code does not follow Intel documentation: It misses some things
and does other, undocumented things. This causes wrong backlight values in
certain conditions. Instead of adding tricky code handling badly documented
and rare corner cases, don't handle combination mode specially at all. This
way PCI_LBPC is never touched and weird things shouldn't happen.

If combination mode is enabled, then the only downside is that changing the
brightness has a greater granularity (the LBPC value), but LBPC is at most
254 and the maximum is in the thousands, so this is no real functional loss.

A potential problem with not handling combined mode is that a brightness of
max * PCI_LBPC is not bright enough. However, this is very unlikely because
from the documentation LBPC seems to act as a scaling factor and doesn't look
like it's supposed to be changed after boot. The value at boot should always
result in a bright enough screen.

IMPORTANT: However, although usually the above is true, it may not be when
people ran an older (2.6.37) kernel which messed up the LBPC register, and
they are unlucky enough to have a BIOS that saves and restores the LBPC value.
Then a good kernel may seem to not work: Max brightness isn't bright enough.
If this happens people should boot back into the old kernel, set brightness
to the maximum, and then reboot. After that everything should be fine.

For more information see the below links. This fixes bugs:

  http://bugzilla.kernel.org/show_bug.cgi?id=23472
  http://bugzilla.kernel.org/show_bug.cgi?id=25072Signed-off-by: NIndan Zupancic <indan@nul.nu>
Tested-by: NAlex Riesen <raa.lkml@gmail.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Share the lid detection code for the all panels for consistent behaviour
and a single place to add the eventual quirks for crap hardware.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>

... and not if the maximum is non-zero. This fixes the typo introduced
in 47356eb6 and preserves the backlight value from boot.

[ickle: My thanks also to Indan Zupancic for diagnosing the original
        regression and suggesting the appropriate fix.]
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org # after 47356eb6

By tracking the current status of the backlight we can prevent recording
the value of the current backlight when we have disabled it. And so
prevent restoring it to 'off' after an unbalanced sequence of
intel_lvds_disable/enable.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=22672Tested-by: NAlex Riesen <raa.lkml@gmail.com>
Tested-by: NLarry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org

After a GPU reset, the backlight controller registers may be also reset
to 0. In that case we should restore those to the original values
programmed by the BIOS. Note that we still lack the code to handle the
case where the BIOS failed to program those registers at all...
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>

Avoid confusion between i965g meaning broadwater and the gen4+ chipset
families.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>

There were two instances of code to control the panel backlight and
neither handled the complete set of device variations.

Fixes:

  Bug 29716 - [GM965] Regression: Backlight resets to minimum when changing resolution
  https://bugs.freedesktop.org/show_bug.cgi?id=29716

And a bug on one of my PineView boxes which overflowed the backlight
value.

Incorporates part of a similar patch by Matthew Garrett that exposes a
native Intel backlight controller.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>

v2: Hook in DP paths to keep FULLSCREEN panel fitting on eDP.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NZhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: NEric Anholt <eric@anholt.net>