Re: [PATCH 1/2] drm/i915: Refuse modes with hdisplay==4096 on pre-HSW DP

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Jul 29, 2019 at 12:11:58PM -0700, Manasi Navare wrote:
> On Thu, Jul 18, 2019 at 05:43:39PM +0300, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > The DP port/pipe goes wonky if we try to use timings with
> > hdisplay==4096 on pre-HSW platforms. The link fails to train
> > and the pipe may not signal vblank interrupts. On HDMI such at
> > mode works just fine (tested on ELK/SNB/CHV). So let's refuse
> > such modes on DP on older platforms.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Makes sense if the link is not able to get trained that we reject this mode
> 
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp.c | 25 +++++++++++++++++++++++++
> >  1 file changed, 25 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 0eb5d66f87a7..c96030761eae 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -493,6 +493,25 @@ int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
> >  	return 0;
> >  }
> >  
> > +static bool intel_dp_hdisplay_bad(struct drm_i915_private *dev_priv,
> > +				  int hdisplay)
> > +{
> > +	/*
> > +	 * Older platforms don't like hdisplay==4096 with DP.
> > +	 *
> > +	 * On ILK/SNB/IVB the pipe seems to be somewhat running (scanline
> > +	 * and frame counter increment), but we don't get vblank interrupts,
> > +	 * and the pipe underruns immediately. The link also doesn't seem
> > +	 * to get trained properly.
> > +	 *
> > +	 * On CHV the vblank interrupts don't seem to disappear but
> > +	 * otherwise the symptoms are similar.
> > +	 *
> > +	 * TODO: confirm the behaviour on HSW+
> > +	 */
> > +	return hdisplay == 4096 && !HAS_DDI(dev_priv);
> > +}
> > +
> >  static enum drm_mode_status
> >  intel_dp_mode_valid(struct drm_connector *connector,
> >  		    struct drm_display_mode *mode)
> > @@ -528,6 +547,9 @@ intel_dp_mode_valid(struct drm_connector *connector,
> >  	max_rate = intel_dp_max_data_rate(max_link_clock, max_lanes);
> >  	mode_rate = intel_dp_link_required(target_clock, 18);
> >  
> > +	if (intel_dp_hdisplay_bad(dev_priv, mode->hdisplay))
> > +		return MODE_H_ILLEGAL;
> > +
> >  	/*
> >  	 * Output bpp is stored in 6.4 format so right shift by 4 to get the
> >  	 * integer value since we support only integer values of bpp.
> > @@ -2208,6 +2230,9 @@ intel_dp_compute_config(struct intel_encoder *encoder,
> >  	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLCLK)
> >  		return -EINVAL;
> >  
> > +	if (intel_dp_hdisplay_bad(dev_priv, adjusted_mode->crtc_hdisplay))
> > +		return -EINVAL;
> 
> Why would we need another check in compute_config() since the mode would have been
> rejected already in intel_dp_mode_valid()

The connector .mode_valid() won't be called for setcrtc/atomic ioctls.
It's only used to filter out the modes from the connector's mode list.

> 
> Manasi
> 
> > +
> >  	ret = intel_dp_compute_link_config(encoder, pipe_config, conn_state);
> >  	if (ret < 0)
> >  		return ret;
> > -- 
> > 2.21.0
> > 
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ville Syrjälä
Intel
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