[Intel-gfx] [PATCH v3] drm/i915/display: Exit PSR when doing async flips
Ville Syrjälä
ville.syrjala at linux.intel.com
Fri Nov 5 17:55:20 UTC 2021
On Fri, Nov 05, 2021 at 05:44:21PM +0000, Souza, Jose wrote:
> On Fri, 2021-11-05 at 15:46 +0200, Ville Syrjälä wrote:
> > On Thu, Nov 04, 2021 at 05:56:52PM +0000, Souza, Jose wrote:
> > > On Thu, 2021-11-04 at 16:10 +0200, Ville Syrjälä wrote:
> > > > On Tue, Nov 02, 2021 at 12:32:14PM -0700, José Roberto de Souza wrote:
> > > > > Changing the buffer in the middle of the scanout then entering an
> > > > > period of flip idleness will cause part of the previous buffer being
> > > > > diplayed to user when PSR is enabled.
> > > > >
> > > > > So here disabling PSR and scheduling activation during the next
> > > > > sync flip.
> > > > >
> > > > > The async flip check that we had in PSR compute is not executed at
> > > > > every flip so it was not doing anything useful and is also being
> > > > > dropped here.
> > > > >
> > > > > v2:
> > > > > - scheduling the PSR work in _intel_psr_post_plane_update()
> > > > >
> > > > > v3:
> > > > > - only re enabling PSR when doing a sync flip
> > > > >
> > > > > Cc: Karthik B S <karthik.b.s at intel.com>
> > > > > Cc: Vandita Kulkarni <vandita.kulkarni at intel.com>
> > > > > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > > > Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > > > > Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
> > > > > ---
> > > > > drivers/gpu/drm/i915/display/intel_psr.c | 37 ++++++++++++++----------
> > > > > 1 file changed, 21 insertions(+), 16 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/i915/display/intel_psr.c b/drivers/gpu/drm/i915/display/intel_psr.c
> > > > > index 9d589d471e335..b8fac53d57df1 100644
> > > > > --- a/drivers/gpu/drm/i915/display/intel_psr.c
> > > > > +++ b/drivers/gpu/drm/i915/display/intel_psr.c
> > > > > @@ -731,12 +731,6 @@ static bool intel_psr2_sel_fetch_config_valid(struct intel_dp *intel_dp,
> > > > > return false;
> > > > > }
> > > > >
> > > > > - if (crtc_state->uapi.async_flip) {
> > > > > - drm_dbg_kms(&dev_priv->drm,
> > > > > - "PSR2 sel fetch not enabled, async flip enabled\n");
> > > > > - return false;
> > > > > - }
> > > > > -
> > > > > /* Wa_14010254185 Wa_14010103792 */
> > > > > if (IS_TGL_DISPLAY_STEP(dev_priv, STEP_A0, STEP_C0)) {
> > > > > drm_dbg_kms(&dev_priv->drm,
> > > > > @@ -1780,36 +1774,47 @@ void intel_psr_pre_plane_update(struct intel_atomic_state *state,
> > > > > if (psr->enabled && needs_to_disable)
> > > > > intel_psr_disable_locked(intel_dp);
> > > > >
> > > > > + if (psr->enabled && crtc_state->uapi.async_flip)
> > > > > + intel_psr_exit(intel_dp);
> > > > > +
> > > > > mutex_unlock(&psr->lock);
> > > > > }
> > > > > }
> > > > >
> > > > > static void _intel_psr_post_plane_update(const struct intel_atomic_state *state,
> > > > > - const struct intel_crtc_state *crtc_state)
> > > > > + const struct intel_crtc_state *old_crtc_state,
> > > > > + const struct intel_crtc_state *new_crtc_state)
> > > >
> > > > Might make sense to change this to match how psr_pre_plane_update()
> > > > works these days.
> > >
> > > Will do as follow up.
> > >
> > > >
> > > > > {
> > > > > struct drm_i915_private *dev_priv = to_i915(state->base.dev);
> > > > > struct intel_encoder *encoder;
> > > > >
> > > > > - if (!crtc_state->has_psr)
> > > > > + if (!new_crtc_state->has_psr)
> > > > > return;
> > > > >
> > > > > for_each_intel_encoder_mask_with_psr(state->base.dev, encoder,
> > > > > - crtc_state->uapi.encoder_mask) {
> > > > > + new_crtc_state->uapi.encoder_mask) {
> > > > > struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
> > > > > struct intel_psr *psr = &intel_dp->psr;
> > > > >
> > > > > mutex_lock(&psr->lock);
> > > > >
> > > > > - drm_WARN_ON(&dev_priv->drm, psr->enabled && !crtc_state->active_planes);
> > > > > + drm_WARN_ON(&dev_priv->drm, psr->enabled &&
> > > > > + !new_crtc_state->active_planes);
> > > > >
> > > > > /* Only enable if there is active planes */
> > > > > - if (!psr->enabled && crtc_state->active_planes)
> > > > > - intel_psr_enable_locked(intel_dp, crtc_state);
> > > > > + if (!psr->enabled && new_crtc_state->active_planes)
> > > > > + intel_psr_enable_locked(intel_dp, new_crtc_state);
> > > >
> > > > What prevents this guy from activating PSR while we're doing
> > > > an async flip?
> > >
> > > enabled != active, when doing a async flip it will set active = false but enabled will be kept on.
> >
> > intel_psr_enable_locked() calls intel_psr_activate() uncoditionally.
> > There is no active=false thing anywhere that I can see.
> >
> > >
> > > And to change the number of active_planes it will need to do a sync flip, so we are safe.
> >
> > Why would the number of active planes need to change for this
> > to get called?
>
> If CRTC is left on but the number of planes goes to 0, PSR is disabled.
> Then it is enabled again if the number of planes goes to 1 or more.
>
> >
> > I guess maybe there's some reason why this can't happen but it is
> > entirely non-obvious when reading this code. Also seems pretty
> > fragile if some other code now changes and suddenly causes this
> > to get called. In fact from the looks of things the only thing
> > needed would be for someone to call intel_psr_disable_locked()
> > so that psr->enabled gets cleared.
>
> If someone calls intel_psr_disable_locked() then in the next flip the code above will indeed enable it again but as PSR takes at least 2 frames to
> actually activate after registers are programmed, we are safe. (see PSR2 EDP_PSR2_FRAME_BEFORE_SU and PSR1 psr_compute_idle_frames())
>
> Then on the next async flip, it will exited again and active set to false.
>
> >
> > I might suggest adding crtc_state->psr_active or soemthing along
> > those lines to make it obvious when we want to have psr logically
> > enabled, but actually inactive.
>
> Because of the invalidate frontbuffer rendering cases, we can't keep PSR status in atomic state.
Not fully. But it shouldn't prevent us from having something there as
well. So if crtc_state says to not activate PSR then don't, otherwise
let it activate/deactive as needed based on frontbuffer activity.
ATM it seems to be kind of ad-hoc when we fully disable vs. just
deactivate PSR. Dunno how feasible it would be to make that either:
a) logically enable/disable PSR only during full modesets, and
otherwise just activate/deactivate as needed whether it be due to
stuff we can calculate based on crtc_state (eg. active_planes or
async_flip) or frontbuffer activity
or
b) always logically enable/disable PSR based on stuff we can calculate
from the crtc state, and leave the activate/deactivate stuff to only
frontbuffer rendering activity
Although there is also the AUX vs. PSR case to consider, but looks like
that is still not fixed.
--
Ville Syrjälä
Intel
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