[Intel-gfx] [PATCH] drm/i915/bxt: Don't save/restore eDP panel power during suspend (v3)

[Daniel Vetter]

On Thu, Jan 07, 2016 at 11:40:22AM +0200, Jani Nikula wrote:
> On Thu, 07 Jan 2016, Daniel Vetter <daniel at ffwll.ch> wrote:
> > On Thu, Jan 07, 2016 at 10:15:00AM +0200, Jani Nikula wrote:
> >> On Wed, 06 Jan 2016, Matt Roper <matthew.d.roper at intel.com> wrote:
> >> > Our attempts save/restore panel power state in i915_suspend.c are
> >> > causing unclaimed register warnings on BXT since the registers for this
> >> > platform differ from older platforms.
> >> >
> >> > The big hammer suspend/resume shouldn't be necessary for PP since the
> >> > connector/encoder hooks should already handle this.  In theory we could
> >> > remove this for all platforms, but in practice it's likely that would
> >> > cause some regressions since older platforms with LVDS may have
> >> > incomplete PP handling.  For now we'll leave the PCH save/restore alone
> >> > and change the non-PCH branch to only operate on gen <= 4 so that BXT
> >> > and future platforms aren't included.
> >> >
> >> > v2: Typo fix: s/||/&&/
> >> >
> >> > v3: Change non-PCH condition to a gen <= 4 test rather than listing
> >> >     VLV/CHV/BXT as specific platforms to exclude; should be more
> >> >     future-proof as we add new platforms.  (Daniel)
> >> >
> >> > Cc: Vandana Kannan <vandana.kannan at intel.com>
> >> > Cc: Jani Nikula <jani.nikula at linux.intel.com>
> >> > Cc: Daniel Vetter <daniel at ffwll.ch>
> >> > Cc: drm-intel-fixes at lists.freedesktop.org
> >> > Signed-off-by: Matt Roper <matthew.d.roper at intel.com>
> >> > ---
> >> > Although it's the direction we want to move, I'm not brave enough to blow away
> >> > the entire PP save/restore for all platforms since I don't have the HW
> >> > necessary to deal with the regressions that might pop up.  The consensus on IRC
> >> > is that there probably will be a few regressions when we do that, so I'd rather
> >> > have people with appropriate platform access make those changes.
> >>
> >> This is the first step we want to take anyway.
> >>
> >> Reviewed-by: Jani Nikula <jani.nikula at intel.com>
> >
> > Just looked at this some more, and the code here is the only code that
> > restores PP registers. Except for vlv/chv, where we have a call to
> > intel_dp_init_panel_power_sequencer_registers in vlv_power_sequencer_pipe.
> >
> > I think we first need to sprinkle more calls to restore PP registers
> > around before we can disable this here for bxt. This patch here just
> > papers over a legit bug, without fixing it really.
>
> No, this patch doesn't paper over anything. The code that gets run for
> Broxton before this patch doesn't save/restore any meaningful registers
> that could possibly help with PP. This fixes unclaimed register
> read/writes, and it's a valid fix as such.
>
> The commit message should probably be fixed to say that we're not there
> yet for Broxton with the hooks. But IMO this patch is a valid fix and
> orthogonal to the issue of fixing the hooks.

The hooks are good enough, at least they work for vlv/chv. If we can't fix
up PP restoring for bxt right away because it's too much work I think we
should at least put int a FIXME. Otherwise we'll promptly forget about
this again, invalidating the value unclaimed register access provides as a
hint that we haven't yet completed some crucial bxt enabling work.

Also, we need a jira to keep track of this. Adding Imre/Annie for that.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch