Re: [PATCH] drm/i915/display: Prevent DC6 while vblank is enabled for Panel Replay

["Hogander, Jouni" <jouni.hogander@intel.com>]

On Wed, 2024-09-11 at 16:00 +0300, Ville Syrjälä wrote:
> On Wed, Sep 11, 2024 at 03:40:15PM +0300, Jouni Högander wrote:
> > We need to block DC6 entry in case of Panel Replay as enabling VBI
> > doesn't
> > prevent DC6 in case of Panel Replay.
> 
> This doesn't make sense to me. I *think* we are currently
> supposed to always operate in the "main link on" mode for panel
> replay.

This is not true. Check bspec 68920:

"When performing PR on an eDP port the Source will allow advanced link
power management (ALPM) to turn the Main Link OFF when not sending an
SDP or update region."

And if you check block_dc6_needed in my patch that is checking eDP.

I was originally planning to handle this by preventing PR entry when
VBLANK is enabled, but that would be more expensive from power
managements point of view -> decided to go with blocking DC6.

BR,

Jouni Högander

> But if we enter DC6 then for sure the main link will be turned off.
> Also DC6 is a superset of DC5, so how can we enter DC6 if we can't
> even enter DC5?
> 
> > This causes problems if user-space is
> > polling for vblank events.
> > 
> > Fix this by setting target DC state as DC_STATE_EN_UPTO_DC5 when
> > both
> > source and sink are supporting eDP Panel Replay and VBI is enabled.
> > 
> > Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2296
> > Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
> > ---
> >  .../gpu/drm/i915/display/intel_display_core.h |  2 +
> >  .../gpu/drm/i915/display/intel_display_irq.c  | 48
> > +++++++++++++++++++
> >  2 files changed, 50 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_core.h
> > b/drivers/gpu/drm/i915/display/intel_display_core.h
> > index 0a711114ff2b4..0707bc2047931 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_core.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_core.h
> > @@ -457,6 +457,8 @@ struct intel_display {
> >                 /* For i915gm/i945gm vblank irq workaround */
> >                 u8 vblank_enabled;
> >  
> > +               struct work_struct vblank_work;
> > +
> >                 u32 de_irq_mask[I915_MAX_PIPES];
> >                 u32 pipestat_irq_mask[I915_MAX_PIPES];
> >         } irq;
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_irq.c
> > b/drivers/gpu/drm/i915/display/intel_display_irq.c
> > index 8f13f148c73e3..96abfb356349e 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_irq.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display_irq.c
> > @@ -15,6 +15,7 @@
> >  #include "intel_display_irq.h"
> >  #include "intel_display_trace.h"
> >  #include "intel_display_types.h"
> > +#include "intel_dp.h"
> >  #include "intel_dp_aux.h"
> >  #include "intel_dsb.h"
> >  #include "intel_fdi_regs.h"
> > @@ -1361,9 +1362,47 @@ static bool gen11_dsi_configure_te(struct
> > intel_crtc *intel_crtc,
> >         return true;
> >  }
> >  
> > +static void intel_display_vblank_work(struct work_struct *work)
> > +{
> > +       struct intel_display *display =
> > +               container_of(work, typeof(*display),
> > irq.vblank_work);
> > +       struct drm_i915_private *i915 = to_i915(display->drm);
> > +
> > +       /*
> > +        * NOTE: intel_display_power_set_target_dc_state is used
> > only by PSR
> > +        * code for DC3CO handling. DC3CO target states is
> > currently disabled in
> > +        * PSR code. If DC3CO is taken into use we need take that
> > into account
> > +        * here as well.
> > +        */
> > +       intel_display_power_set_target_dc_state(i915, display-
> > >irq.vblank_enabled ?
> > +                                               DC_STATE_EN_UPTO_DC
> > 5 : DC_STATE_EN_UPTO_DC6);
> > +}
> > +
> > +/*
> > + * We need to block DC6 entry in case of Panel Replay as enabling
> > VBI doesn't
> > + * prevent DC6 in case of Panel Replay. This causes problems if
> > user-space is
> > + * polling for vblank events.
> > + */
> > +static bool block_dc6_needed(struct intel_display *display)
> > +{
> > +       struct intel_encoder *encoder;
> > +
> > +       for_each_intel_encoder_with_psr(display->drm, encoder) {
> > +               struct intel_dp *intel_dp =
> > enc_to_intel_dp(encoder);
> > +
> > +               if (!intel_dp_is_edp(intel_dp))
> > +                       continue;
> > +
> > +               if (CAN_PANEL_REPLAY(intel_dp))
> > +                       return true;
> > +       }
> > +       return false;
> > +}
> > +
> >  int bdw_enable_vblank(struct drm_crtc *_crtc)
> >  {
> >         struct intel_crtc *crtc = to_intel_crtc(_crtc);
> > +       struct intel_display *display = to_intel_display(crtc);
> >         struct drm_i915_private *dev_priv = to_i915(crtc-
> > >base.dev);
> >         enum pipe pipe = crtc->pipe;
> >         unsigned long irqflags;
> > @@ -1371,6 +1410,9 @@ int bdw_enable_vblank(struct drm_crtc *_crtc)
> >         if (gen11_dsi_configure_te(crtc, true))
> >                 return 0;
> >  
> > +       if (block_dc6_needed(display) && display-
> > >irq.vblank_enabled++ == 0)
> > +               schedule_work(&display->irq.vblank_work);
> > +
> >         spin_lock_irqsave(&dev_priv->irq_lock, irqflags);
> >         bdw_enable_pipe_irq(dev_priv, pipe, GEN8_PIPE_VBLANK);
> >         spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
> > @@ -1436,6 +1478,7 @@ void ilk_disable_vblank(struct drm_crtc
> > *crtc)
> >  void bdw_disable_vblank(struct drm_crtc *_crtc)
> >  {
> >         struct intel_crtc *crtc = to_intel_crtc(_crtc);
> > +       struct intel_display *display = to_intel_display(crtc);
> >         struct drm_i915_private *dev_priv = to_i915(crtc-
> > >base.dev);
> >         enum pipe pipe = crtc->pipe;
> >         unsigned long irqflags;
> > @@ -1446,6 +1489,9 @@ void bdw_disable_vblank(struct drm_crtc
> > *_crtc)
> >         spin_lock_irqsave(&dev_priv->irq_lock, irqflags);
> >         bdw_disable_pipe_irq(dev_priv, pipe, GEN8_PIPE_VBLANK);
> >         spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
> > +
> > +       if (block_dc6_needed(display) && --display-
> > >irq.vblank_enabled == 0)
> > +               schedule_work(&display->irq.vblank_work);
> >  }
> >  
> >  void vlv_display_irq_reset(struct drm_i915_private *dev_priv)
> > @@ -1871,4 +1917,6 @@ void intel_display_irq_init(struct
> > drm_i915_private *i915)
> >                 i915->display.irq.display_irqs_enabled = false;
> >  
> >         intel_hotplug_irq_init(i915);
> > +
> > +       INIT_WORK(&i915->display.irq.vblank_work,
> > intel_display_vblank_work);
> >  }
> > -- 
> > 2.34.1
>