This patch adds the ability to override the typical display timing for a
given panel. This is useful for devices which have timing constraints
that do not apply across the entire display driver (eg: to avoid
crosstalk between panel and digitizer on certain laptops). The rules are
as follows:

- panel must not specify fixed mode (since the override mode will
  either be the same as the fixed mode, or we'll be unable to
  check the bounds of the overried)
- panel must specify at least one display_timing range which will be
  used to ensure the override mode fits within its bounds

Changes in v2:
 - Parse the full display-timings node (using the native-mode) (Rob)
Changes in v3:
 - No longer parse display-timings subnode, use panel-timing (Rob)
Changes in v4:
 - Don't add mode from timing if override was specified (Thierry)
 - Add warning if timing and fixed mode was specified (Thierry)
 - Don't add fixed mode if timing was specified (Thierry)
 - Refactor/rename a bit to avoid extra indentation from "if" tests
 - i should be unsigned (Thierry)
 - Add annoying WARN_ONs for some cases (Thierry)
 - Simplify 'No display_timing found' handling (Thierry)
 - Rename to panel_simple_parse_override_mode() (Thierry)
Changes in v5:
 - Added Heiko's Tested-by
Changes in v6:
 - Rebased to drm-misc next
 - Added tags

Cc: Doug Anderson <dianders@chromium.org>
Cc: Eric Anholt <eric@anholt.net>
Cc: Heiko Stuebner <heiko@sntech.de>
Cc: Jeffy Chen <jeffy.chen@rock-chips.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Stéphane Marchesin <marcheu@chromium.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: devicetree@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190711203455.125667-2-dianders@chromium.org