In general, the timing diagrams for components specify a minimum time
for power cycling the component. When we remove power from a device we
need to let the device fully discharge and get to a quiescent state
before applying power again. If we power a device on too soon then it
might not have fully powered off and might be in a weird in-between /
invalid state.

eDP panels typically have a time that's at least 500 ms here. You can
see that in Linux's panel-edp driver nearly every device specifies a
"unprepare" time of at least 500 ms. This is a common minimum and the
500 ms is even in the example in the eDP spec.

In Linux, the "panel-edp" driver enforces this delay for its own
control of the regulator, but the "panel-edp" driver can't do anything
about other control of the regulator (for instance, by the touchpanel
driver).

Let's add 500 ms as a board constraint for the regulator that's used
for eDP/touchpanel on trogdor boards. If a given trogdor board stuffs
only panels that can use a shorter time or stuff some panels that need
a larger time then they can manually adjust this timing.

We'll only do this minimum delay for trogdor devices with eDP (ones
that use either bridge chip), not for devices with MIPI panels. MIPI
panels could have similar constraints but the 500 ms isn't necessarily
as standard and there are no known cases where this delay is needed.

For most trogdor boards, this doesn't actually seem to affect anything
when testing against shipping Linux. However, with pazqel360 it seems
that this does make a difference. It seems that the touchscreen on
this board _also_ needs some time for the regulator to discharge. That
time is much less than 500 ms, so we'll just put the eDP panel 500 ms
in there since the board constraint should be the "max" of the
components.
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221209091234.v3.2.I65ac577411b017eff50e7a4fda254e5583ccdc48@changeid