[PATCH v2 2/2] drm/i915/psr: Do not disable Panel Replay if PSR2 is disabled

[Ville Syrjälä]

On Thu, Jul 10, 2025 at 05:27:13PM -0400, Rodrigo Vivi wrote:
> On Thu, Jul 10, 2025 at 11:09:42PM +0300, Ville Syrjälä wrote:
> > On Thu, Jul 10, 2025 at 11:42:52AM -0400, Rodrigo Vivi wrote:
> > > On Wed, Jul 09, 2025 at 06:11:17PM +0000, Hogander, Jouni wrote:
> > > > On Wed, 2025-07-09 at 20:03 +0300, Ville Syrjälä wrote:
> > > > > On Wed, Jul 09, 2025 at 10:57:58AM +0300, Jouni Högander wrote:
> > > > > > Currently disabling PSR2 via enable_psr module parameter causes
> > > > > > Panel
> > > > > > Replay being disabled as well. This patch changes this by still
> > > > > > allowing
> > > > > > Panel Replay even if PSR2 is disabled.
> > > > > > 
> > > > > > After this patch enable_psr module parameter values are:
> > > > > > 
> > > > > > -1 = PSR1 : yes, PSR2 = yes, Panel Replay : yes
> > > > > >  0 = PSR1 : no,  PSR2 = no,  Panel Replay : no
> > > > > >  1 = PSR1 : yes, PSR2 = no,  Panel Replay : yes
> > > > > >  2 = PSR1 : yes, PSR2 = yes, Panel Replay : no
> > > > > >  3 = PSR1 : yes, PSR2 = no,  Panel Replay : no
> > > > > > 
> > > > > > I.e. values different than -1 and 0 are handled as bitmasks where
> > > > > > BIT0
> > > > > > disables PSR2 and BIT1 disables Panel Replay.
> > > > > > 
> > > > > > v2:
> > > > > >   - make it more clear that enable_psr is bitmask for disabling
> > > > > > different
> > > > > >     PSR modes
> > > > > > 
> > > > > > Signed-off-by: Jouni Högander <jouni.hogander at intel.com>
> > > > > > ---
> > > > > >  .../drm/i915/display/intel_display_params.c   |  6 ++---
> > > > > >  drivers/gpu/drm/i915/display/intel_psr.c      | 22 ++++++++++++++-
> > > > > > ----
> > > > > >  2 files changed, 19 insertions(+), 9 deletions(-)
> > > > > > 
> > > > > > diff --git a/drivers/gpu/drm/i915/display/intel_display_params.c
> > > > > > b/drivers/gpu/drm/i915/display/intel_display_params.c
> > > > > > index 75316247ee8a..195af19ece5f 100644
> > > > > > --- a/drivers/gpu/drm/i915/display/intel_display_params.c
> > > > > > +++ b/drivers/gpu/drm/i915/display/intel_display_params.c
> > > > > > @@ -116,9 +116,9 @@ intel_display_param_named_unsafe(enable_fbc,
> > > > > > int, 0400,
> > > > > >  	"(default: -1 (use per-chip default))");
> > > > > >  
> > > > > >  intel_display_param_named_unsafe(enable_psr, int, 0400,
> > > > > > -	"Enable PSR "
> > > > > > -	"(0=disabled, 1=enable up to PSR1, 2=enable up to PSR2) "
> > > > > > -	"Default: -1 (use per-chip default)");
> > > > > > +	"Enable PSR (0=disabled, 1=disable PSR2 (BIT0), 2=disable
> > > > > > Panel Replay (BIT1))."
> > > > > > +	"Values different from 0 and -1 are handled as bitmask to
> > > > > > disable different PSR modes."
> > > > > > +	"E.g. value 3 disables both PSR2 and Panel Replay.
> > > > > > Default: -1 (use per-chip default)");
> > > > > 
> > > > > This thing is very unintuitive. Why don't we just get replace it
> > > > > with a new disable_psr modparam that is clearly just a bitmask of
> > > > > what to disable?
> > > > 
> > > > I was thinkinig we should keep it backward compatible. I know this
> > > > parameter is in use.
> > > 
> > > I agree on keeping this backward compatible.
> > 
> > IMO it's an unusable mess so I wouldn't bother trying to preserve it.
> > The only value that seems to make any sense currently is =0. 
> 
> fair enough. what about simply removing all the options entirely?
> enable_psr=0 keeps disabling it, otherwise enabled it. And we reduce
> all the knobs option. Afterall, this should be our end goal anyway.
> 
> > If I
> > need to use any other value I always give up immediately and just
> > hack the code instead.
> 
> Well, the param actually exists for us to request reporters to try
> different config. The devs can always modify the code.
> 
> Question now is, are all these variants useful for collecting debug
> information of some sort?
> 
> If so, as long as it is documented and we can ask different values,
> we should be good.
> 
> > 
> > If we keep calling it 'enable_psr' then it should clearly be a
> > bitmask of things to *enable*, not things to *disable*.
> > 
> > > 
> > > Also our experience with disable_power_well shows that negative
> > > name in the parameter can be much more unintuitive and confusing.
> > 
> > That one is rather different because it doesn't "disable power wells"
> > but rather it "disables power well disabling". But yes, it is a very
> > poor name as well.
> > 
> > Calling it "enable_power_wells" wouldn't really help though.
> > It should perhaps be something more like 'dont_disable_power_wells'
> > or 'keep_power_wells_on'.
> 
> okay, fair enough, disable power well is another level of complication.
> 
> back to disable_psr idea:
> 
> disable_psr=0 == enable PSR? to me this is already uninituitive anyway.
> disable_psr=1 == disable PSR1?
> disable_psr=2 == disable PSR2? and keep only PSR=1?
> 
> I still don't see a clean obvious intuitive way of handling it.
> Perhaps what I had suggested another day:
> 
> PSR1 = BIT0
> PSR2 = BIT1 (PSR2 infers PSR1 enabled)
> PANEL_REPLAY = BIT2 (also infers PSR1(and 2?) enabled)

With a bitmask I don't think inferring anything is helpful.
If the corresponding bit isn't set then don't use that
mode, period.

Another option would to have a separate named parameter
for each mode. Would be easier to understand but dunno
if we really want to add that many modparams just for this.

> (Peraps even bit3 for early transport?)
> 
> This is backwards compatible because
> 
> 0 = disabled,
> 1 = up to psr1,
> 2 = up to psr2, (no panel replay)
> 3 = up to psr2, (same as 2)
> 4 = panel replay on
> ...
> 
> > 
> > -- 
> > Ville Syrjälä
> > Intel

-- 
Ville Syrjälä
Intel