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

[Hogander, Jouni]

On Thu, 2025-07-10 at 23:09 +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. If I
> need to use any other value I always give up immediately and just
> hack the code instead.

It's unintuitive but not unusable. I have instructed several times bug
reporter to set it to 0/1 to bisect if it's PSR2 problem. We have also
customers using this to disable PSR modes they don't want. As we have
provided this at some point I wouldn't drop it now.

> 
> If we keep calling it 'enable_psr' then it should clearly be a
> bitmask of things to *enable*, not things to *disable*.

Ok, it seems I need inverse the logic to enable rather than disable. I
will do that.

BR,

Jouni Högander

> 
> > 
> > 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'.
>