Re: [PATCH] drm/i915/psr: Request modeset on initial commit to compute PSR state

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 23 Jan 2024, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Tue, Jan 23, 2024 at 07:57:00AM +0000, Hogander, Jouni wrote:
>> On Tue, 2024-01-23 at 09:41 +0200, Ville Syrjälä wrote:
>> > On Tue, Jan 23, 2024 at 09:11:03AM +0200, Jouni Högander wrote:
>> > > We want to request full modeset in initial fast check to force PSR
>> > > state
>> > > computation. Otherwise PSR is not enabled on initial commit but on
>> > > first
>> > > commit with modeset or fastset. With this change Initial commit
>> > > will still
>> > > end up using fastset (unless something else requires full modeset)
>> > > as PSR
>> > > parameters are not anymore part of intel_pipe_config_compare.
>> > 
>> > I think I'd prefer to go the oppostie direction and try to get all
>> > the full modeset stuff out from the initial commit. The only reason
>> > the initial commit was introduced was to compute the plane states
>> > due to lack of readout, and then it got extended due to various other
>> > hacks. Our goal is to inherit the state from the BIOS so ideally
>> > the whole initial_commit thing wouldn't even exist.
>> 
>> Bios doesn't enable PSR. Do you think this would be better approach ?:
>> 
>> https://patchwork.freedesktop.org/patch/575368/?series=129023&rev=1
>> 
>> What we just need is something triggering intel_psr_compute_config +
>> psr enable. Maybe that could be separate function doing both and call
>> that from intel_initial_commit. If/when we get rid of that
>> intel_initial_commit: this function would be called by that new thing.
>
> I don't think we should do anything at all. PSR will get enabled by the
> first proper commit, if possible.

In general, I'm leaning the same way. Priorities:

1) Avoid full modeset at probe if at all possible.

2) Taking the above into account, enable as many power saving
   etc. features as possible at probe.

3) If a system needs more power savings (or other fancy features
   enabled), a) have them enabled by BIOS/GOP, or b) have the userspace
   do a modeset post-probe according to its policy. Don't force that
   policy on the kernel.

4) *Maybe* provide a way to force full modeset at probe as a policy
   option.


BR,
Jani.




>
>> 
>> BR,
>> 
>> Jouni Högander
>> 
>> > 
>> > > 
>> > > Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
>> > > 
>> > > Fixes: a480dd59fe25 ("drm/i915/display: No need for full modeset
>> > > due to psr")
>> > > Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
>> > > ---
>> > >  drivers/gpu/drm/i915/display/intel_dp.c  | 8 ++++++++
>> > >  drivers/gpu/drm/i915/display/intel_psr.c | 3 ---
>> > >  drivers/gpu/drm/i915/display/intel_psr.h | 3 +++
>> > >  3 files changed, 11 insertions(+), 3 deletions(-)
>> > > 
>> > > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
>> > > b/drivers/gpu/drm/i915/display/intel_dp.c
>> > > index ab415f41924d..143981b91e8b 100644
>> > > --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> > > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> > > @@ -3326,6 +3326,14 @@ bool intel_dp_initial_fastset_check(struct
>> > > intel_encoder *encoder,
>> > >                 fastset = false;
>> > >         }
>> > >  
>> > > +       if (CAN_PSR(intel_dp)) {
>> > > +               drm_dbg_kms(&i915->drm, "[ENCODER:%d:%s] Forcing
>> > > full modeset to compute PSR state\
>> > > +n",
>> > > +                           encoder->base.base.id, encoder-
>> > > >base.name);
>> > > +               crtc_state->uapi.mode_changed = true;
>> > > +               fastset = false;
>> > > +       }
>> > > +
>> > >         return fastset;
>> > >  }
>> > >  
>> > > diff --git a/drivers/gpu/drm/i915/display/intel_psr.c
>> > > b/drivers/gpu/drm/i915/display/intel_psr.c
>> > > index 1010b8c405df..b6db7dbfaf1a 100644
>> > > --- a/drivers/gpu/drm/i915/display/intel_psr.c
>> > > +++ b/drivers/gpu/drm/i915/display/intel_psr.c
>> > > @@ -173,9 +173,6 @@
>> > >   * irrelevant for normal operation.
>> > >   */
>> > >  
>> > > -#define CAN_PSR(intel_dp) ((intel_dp)->psr.sink_support && \
>> > > -                          (intel_dp)->psr.source_support)
>> > > -
>> > >  #define CAN_PANEL_REPLAY(intel_dp) ((intel_dp)-
>> > > >psr.sink_panel_replay_support && \
>> > >                                     (intel_dp)-
>> > > >psr.source_panel_replay_support)
>> > >  
>> > > diff --git a/drivers/gpu/drm/i915/display/intel_psr.h
>> > > b/drivers/gpu/drm/i915/display/intel_psr.h
>> > > index cde781df84d5..3d9920ebafab 100644
>> > > --- a/drivers/gpu/drm/i915/display/intel_psr.h
>> > > +++ b/drivers/gpu/drm/i915/display/intel_psr.h
>> > > @@ -21,6 +21,9 @@ struct intel_encoder;
>> > >  struct intel_plane;
>> > >  struct intel_plane_state;
>> > >  
>> > > +#define CAN_PSR(intel_dp) ((intel_dp)->psr.sink_support && \
>> > > +                          (intel_dp)->psr.source_support)
>> > > +
>> > >  bool intel_encoder_can_psr(struct intel_encoder *encoder);
>> > >  void intel_psr_init_dpcd(struct intel_dp *intel_dp);
>> > >  void intel_psr_pre_plane_update(struct intel_atomic_state *state,
>> > > -- 
>> > > 2.34.1
>> > 
>> 

-- 
Jani Nikula, Intel