Re: [PATCH 1/5] drm/i915/dp_tunnel: Don't update tunnel state during system resume

[Imre Deak <imre.deak@intel.com>]

On Tue, Feb 24, 2026 at 04:33:58AM +0200, Murthy, Arun R wrote:
> 
> > -----Original Message-----
> > From: Deak, Imre <imre.deak@intel.com>
> > Sent: Monday, February 23, 2026 10:00 PM
> > To: Murthy, Arun R <arun.r.murthy@intel.com>
> > Cc: intel-gfx@lists.freedesktop.org; intel-xe@lists.freedesktop.org
> > Subject: Re: [PATCH 1/5] drm/i915/dp_tunnel: Don't update tunnel state during
> > system resume
> > 
> > On Mon, Feb 23, 2026 at 05:54:38PM +0200, Murthy, Arun R wrote:
> > >
> > > > -----Original Message-----
> > > > From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf
> > > > Of Imre Deak
> > > > Sent: Thursday, February 19, 2026 11:58 PM
> > > > To: intel-gfx@lists.freedesktop.org; intel-xe@lists.freedesktop.org
> > > > Subject: [PATCH 1/5] drm/i915/dp_tunnel: Don't update tunnel state
> > > > during system resume
> > > >
> > > > During system resume, restoring the pre-suspend display state must not fail.
> > > > This requires preserving the sink capabilities from before suspend,
> > > > including the available link bandwidth.
> > > >
> > > I don't see the sink capabilities being stored in this patch.
> > 
> > The sink capabilities are stored in intel_dp and intel_connector, including the
> > maximum link rate and lane count, which determine the link bandwidth. This
> > patch preserves those capabilities across suspend/resume by preventing the
> > tunnel state from being updated during resume.
> > 
> I understand, but what I meant was this patch doesn't handle anything
> on the suspend part but only controls the updates on resume.  So
> explaining what happens on resume is un-necessary.

What happens during resume - restoring the state of display outputs to
the pre-suspend state - is what requires the change in this patch.

The commit message must describe the reason for the change, so this
commit must describe what happens during resume.

> Thanks and Regards,
> Arun R Murthy
> --------------------
> > >
> > > > If these capabilities are not preserved, the restore modeset may
> > > > fail, either due to a missing sink capability or insufficient link bandwidth for
> > the restored mode.
> > > Don't see this in the patch.
> > >
> > > >
> > > > When the sink is connected through a DP tunnel, prevent such
> > > > capability changes by skipping tunnel state updates during resume.
> > > > This also avoids updating the sink state via the tunnel while it is being
> > resumed.
> > > >
> > > > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > > > ---
> > > >  drivers/gpu/drm/i915/display/intel_dp_tunnel.c | 11 ++++++-----
> > > >  1 file changed, 6 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_tunnel.c
> > > > b/drivers/gpu/drm/i915/display/intel_dp_tunnel.c
> > > > index faa2b7a46699d..eb1eed1c8c7bb 100644
> > > > --- a/drivers/gpu/drm/i915/display/intel_dp_tunnel.c
> > > > +++ b/drivers/gpu/drm/i915/display/intel_dp_tunnel.c
> > > > @@ -150,11 +150,9 @@ static int
> > > > allocate_initial_tunnel_bw_for_pipes(struct
> > > > intel_dp *intel_dp, u8 pi
> > > >  			    drm_dp_tunnel_name(intel_dp->tunnel),
> > > >  			    encoder->base.base.id, encoder->base.name,
> > > >  			    ERR_PTR(err));
> > > > -
> > > > -		return err;
> > > >  	}
> > > >
> > > > -	return update_tunnel_state(intel_dp);
> > > > +	return err;
> > > >  }
> > > >
> > > >  static int allocate_initial_tunnel_bw(struct intel_dp *intel_dp, @@
> > > > -200,10
> > > > +198,13 @@ static int detect_new_tunnel(struct intel_dp *intel_dp,
> > > > +struct
> > > > drm_modeset_acqui
> > > >  	}
> > > >
> > > >  	ret = allocate_initial_tunnel_bw(intel_dp, ctx);
> > > > -	if (ret < 0)
> > > > +	if (ret < 0) {
> > > >  		intel_dp_tunnel_destroy(intel_dp);
> > > >
> > > > -	return ret;
> > > > +		return ret;
> > > > +	}
> > > > +
> > > > +	return update_tunnel_state(intel_dp);
> > > >  }
> > > >
> > > >  /**
> > > > --
> > > > 2.49.1
> > >
> > > Thanks and Regards,
> > > Arun R Murthy
> > > --------------------