drm/i915/dp: Perform 30ms delay after source OUI write

drm/i915/dp: Perform 30ms delay after source OUI write

While working on supporting the Intel HDR backlight interface, I noticed
that there's a couple of laptops that will very rarely manage to boot up
without detecting Intel HDR backlight support - even though it's supported
on the system. One example of such a laptop is the Lenovo P17 1st
generation.

Following some investigation Ville Syrjälä did through the docs they have
available to them, they discovered that there's actually supposed to be a
30ms wait after writing the source OUI before we begin setting up the rest
of the backlight interface.

This seems to be correct, as adding this 30ms delay seems to have
completely fixed the probing issues I was previously seeing. So - let's
start performing a 30ms wait after writing the OUI, which we do in a manner
similar to how we keep track of PPS delays (e.g. record the timestamp of
the OUI write, and then wait for however many ms are left since that
timestamp right before we interact with the backlight) in order to avoid
waiting any longer then we need to. As well, this also avoids us performing
this delay on systems where we don't end up using the HDR backlight
interface.

V3:
* Move last_oui_write into intel_dp
V2:
* Move panel delays into intel_pps

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Fixes: 4a8d79901d5b ("drm/i915/dp: Enable Intel's HDR backlight interface (only SDR for now)")
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: <stable@vger.kernel.org> # v5.12+
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211130212912.212044-1-lyude@redhat.com