[RFC 2/4] drm/i915/display/dp: Dont send hotplug event on LT failure

[Almahallawy, Khaled]

On Tue, 2024-02-06 at 15:06 +0000, Murthy, Arun R wrote:
> > -----Original Message-----
> > From: Nikula, Jani <jani.nikula at intel.com>
> > Sent: Tuesday, February 6, 2024 5:10 PM
> > To: Murthy, Arun R <arun.r.murthy at intel.com>; 
> > intel-gfx at lists.freedesktop.org
> > Cc: Deak, Imre <imre.deak at intel.com>; Syrjala, Ville <
> > ville.syrjala at intel.com>;
> > Shankar, Uma <uma.shankar at intel.com>; Murthy, Arun R
> > <arun.r.murthy at intel.com>
> > Subject: Re: [RFC 2/4] drm/i915/display/dp: Dont send hotplug event
> > on LT
> > failure
> > 
> > On Tue, 06 Feb 2024, Arun R Murthy <arun.r.murthy at intel.com> wrote:
> > > On link training failure fallback sequence a hotpplu event was
> > > sent to
> > > the user, but this is not requried as we are not changing the
> > > mode and
> > > instead only changing the link rate and lane count. User has no
> > > dependency with these parameters.
> > > 
> > > Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/display/intel_dp_link_training.c | 5 +----
> > >  1 file changed, 1 insertion(+), 4 deletions(-)
> > > 
> > > diff --git
> > > a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > > b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > > index 1abfafbbfa75..242cb08e9fc4 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > > @@ -1074,8 +1074,6 @@ intel_dp_link_train_phy(struct intel_dp
> > > *intel_dp,  static void
> > > intel_dp_schedule_fallback_link_training(struct intel_dp
> > *intel_dp,
> > >  						     const struct
> > > intel_crtc_state
> > *crtc_state)  {
> > > -	struct intel_connector *intel_connector = intel_dp-
> > > attached_connector;
> > > -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > > 
> > >  	if (!intel_digital_port_connected(&dp_to_dig_port(intel_dp)-
> > > >base)) {
> > >  		lt_dbg(intel_dp, DP_PHY_DPRX, "Link Training failed on
> > disconnected
> > > sink.\n"); @@ -1092,8 +1090,7 @@ static void
> > intel_dp_schedule_fallback_link_training(struct intel_dp *intel_dp,
> > >  		return;
> > >  	}
> > > 
> > > -	/* Schedule a Hotplug Uevent to userspace to start modeset */
> > > -	queue_work(i915->unordered_wq, &intel_connector-
> > > modeset_retry_work);
> > > +	/* TODO: Re-visit, sending hotplug is not required. No need to
> > > +notify user as we are not changing the mode */
> > 
> > Yeah, we're not changing the mode, we're asking the userspace to
> > change the
> > mode.
> As far as I see mode change is not necessity. Link rate and lane
> count change is internal to KMD.

Userspace may need to reprobe again in order to ensure that the resolution/refresh rate still fits within the bandwidth provided by LR/LC.
Also I believe this part works with DP1.4 LT fallback when we tested
recently.

Thanks
Khaled
> 
> Thanks and Regards,
> Arun R Murthy
> --------------------
> > BR,
> > Jani.
> > 
> > >  }
> > > 
> > >  /* Perform the link training on all LTTPRs and the DPRX on a
> > > link. */
> > 
> > --
> > Jani Nikula, Intel