[PATCH 18/19] drm/i915/dp: Suspend/resume DP tunnels

[Imre Deak]

On Wed, Jan 31, 2024 at 06:18:22PM +0200, Ville Syrjälä wrote:
> On Tue, Jan 23, 2024 at 12:28:49PM +0200, Imre Deak wrote:
> > Suspend and resume DP tunnels during system suspend/resume, disabling
> > the BW allocation mode during suspend, re-enabling it after resume. This
> > reflects the link's BW management component (Thunderbolt CM) disabling
> > BWA during suspend. Before any BW requests the driver must read the
> > sink's DPRX capabilities (since the BW manager requires this
> > information, so snoops for it on AUX), so ensure this read takes place.
> 
> Isn't that going to screw up the age old problem of .compute_config()
> potentially failing during the resume modeset if we no longer have
> the same amount of bandwidth available as we had before suspend?
> So far we've been getting away with this exactly by not updating 
> the dpcd stuff before the modeset during resume.

Right, in the case where this would be a problem (so not counting where
the caps haven't been read out yet and so we update here
intel_dp->dpcd), the caps in intel_dp->dpcd will be preserved, not
actually updated with the read-out values, see intel_dp_tunnel_resume()
in patch 11.

The same goes for the tunnel (group) BW: it will not be updated during
resume (by way of the connector/tunnel detection being blocked during
the restore modeset), so the restore modeset should see the same amount
of BW as there was during suspend.

> 
> > 
> > Signed-off-by: Imre Deak <imre.deak at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp.c | 16 +++++++++++-----
> >  1 file changed, 11 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 8ebfb039000f6..bc138a54f8d7b 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -36,6 +36,7 @@
> >  #include <asm/byteorder.h>
> >  
> >  #include <drm/display/drm_dp_helper.h>
> > +#include <drm/display/drm_dp_tunnel.h>
> >  #include <drm/display/drm_dsc_helper.h>
> >  #include <drm/display/drm_hdmi_helper.h>
> >  #include <drm/drm_atomic_helper.h>
> > @@ -3320,18 +3321,21 @@ void intel_dp_sync_state(struct intel_encoder *encoder,
> >  			 const struct intel_crtc_state *crtc_state)
> >  {
> >  	struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
> > -
> > -	if (!crtc_state)
> > -		return;
> > +	bool dpcd_updated = false;
> >  
> >  	/*
> >  	 * Don't clobber DPCD if it's been already read out during output
> >  	 * setup (eDP) or detect.
> >  	 */
> > -	if (intel_dp->dpcd[DP_DPCD_REV] == 0)
> > +	if (crtc_state && intel_dp->dpcd[DP_DPCD_REV] == 0) {
> >  		intel_dp_get_dpcd(intel_dp);
> > +		dpcd_updated = true;
> > +	}
> >  
> > -	intel_dp_reset_max_link_params(intel_dp);
> > +	intel_dp_tunnel_resume(intel_dp, dpcd_updated);
> > +
> > +	if (crtc_state)
> > +		intel_dp_reset_max_link_params(intel_dp);
> >  }
> >  
> >  bool intel_dp_initial_fastset_check(struct intel_encoder *encoder,
> > @@ -5973,6 +5977,8 @@ void intel_dp_encoder_suspend(struct intel_encoder *intel_encoder)
> >  	struct intel_dp *intel_dp = enc_to_intel_dp(intel_encoder);
> >  
> >  	intel_pps_vdd_off_sync(intel_dp);
> > +
> > +	intel_dp_tunnel_suspend(intel_dp);
> >  }
> >  
> >  void intel_dp_encoder_shutdown(struct intel_encoder *intel_encoder)
> > -- 
> > 2.39.2
> 
> -- 
> Ville Syrjälä
> Intel