Re: [PATCH 02/14] drm/i915: Reorganize vlv eDP reboot notifier

Daniel Vetter
2014-08-26T13:35:44Z

On Tue, Aug 26, 2014 at 04:21:00PM +0300, Jani Nikula wrote:
> On Tue, 26 Aug 2014, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> > On Tue, Aug 19, 2014 at 10:00:55AM +0300, Jani Nikula wrote:
> >> On Mon, 18 Aug 2014, ville.syrjala@linux.intel.com wrote:
> >> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >> >
> >> > Move the vlv_power_sequencer_pipe() after the IS_VALLEYVIEW() check
> >> > and flatten the rest of the function.
> >>
> >> Please imagine adding another platform there, and realize this just adds
> >> unnecessary churn.
> >
> > I'd just add another reboot notifier then.
>
> Fair enough; it should be vlv_edp_notify_handler then. (No, don't send a
> patch to change that! ;)
>
> > Frankly I don't understand the current one either. Why does it need to
> > set the delay to max for instance? And does this mean that the
> > PANEL_POWER_RESET bit doesn't actually work as advertised in the docs?
>
> *shrug* experimental evidence?
>
> commit 01527b3127997ef6370d5ad4fa25d96847fbf12a
> Author: Clint Taylor <clinton.a.taylor@intel.com>
> Date: Mon Jul 7 13:01:46 2014 -0700
>
> drm/i915/vlv: T12 eDP panel timing enforcement during reboot
>
> The panel power sequencer on vlv doesn't appear to accept changes to its
> T12 power down duration during warm reboots. This change forces a delay
> for warm reboots to the T12 panel timing as defined in the VBT table for
> the connected panel.

So if I remember this piece of lore correctly in the past the pp was
pessimistic, and enforced this delay on resume/boot-up, assuming you've
shut down _right_ before the machine was lit up again. Apparently people
where unhappy with that enforced delay and it was ditched on vlv, but then
it broke panels if you actually managed to reboot quickly enough.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch