Re: [PATCH] drm/i915: Improve DP downstream HPD handling

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: "Pandiyan, Dhinakaran" <dhinakaran.pandiyan@intel.com>
Cc: "intel-gfx@lists.freedesktop.org"
	<intel-gfx@lists.freedesktop.org>,
	"dwmw2@infradead.org" <dwmw2@infradead.org>,
	"pablodebiase@nanalysis.com" <pablodebiase@nanalysis.com>
Subject: Re: [PATCH] drm/i915: Improve DP downstream HPD handling
Date: Fri, 27 Oct 2017 12:39:57 +0300	[thread overview]
Message-ID: <20171027093957.GY10981@intel.com> (raw)
In-Reply-To: <1509066685.14402.34.camel@dk-H97M-D3H>

On Fri, Oct 27, 2017 at 12:48:39AM +0000, Pandiyan, Dhinakaran wrote:
> 
> On Thu, 2017-10-26 at 22:41 +0300, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > DP dongles may signal downstream HPD via short HPD pulses. Setting the
> > sink to DPMS off apparently kills the downstream HPD (at least on my
> > DP->VGA dongle), so skip the DPMS off for such dongles when we turn
> > off the port.
> > 
> > Cc: David Woodhouse <dwmw2@infradead.org>
> > Cc: Imre Deak <imre.deak@intel.com>
> > Cc: Pablo <pablodebiase@nanalysis.com>
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103472
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99114
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 18 +++++++++++++++++-
> >  1 file changed, 17 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index aa75f55eeb61..6ecc1b532f15 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -2673,6 +2673,21 @@ static void intel_dp_get_config(struct intel_encoder *encoder,
> >  	}
> >  }
> >  
> > +static bool downstream_hpd_needs_d0(struct intel_dp *intel_dp)
> > +{
> > +	/*
> > +	 * DPCD 1.2 should support BRANCH_DEVICE_CTRL, and thus
> > +	 * be capable of signalling downstream hpd with a long pulse.
> > +	 * Whether or not that means D3 is safe to use is not clear,
> > +	 * but let's assume so until proven otherwise.
> > +	 *
> > +	 * FIXME should really check all downstream ports...
> > +	 */
> > +	return intel_dp->dpcd[DP_DPCD_REV] == 0x11 &&
> > +		intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT &&
> > +		intel_dp->downstream_ports[0] & DP_DS_PORT_HPD;
> > +}
> > +
> >  static void intel_disable_dp(struct intel_encoder *encoder,
> >  			     const struct intel_crtc_state *old_crtc_state,
> >  			     const struct drm_connector_state *old_conn_state)
> > @@ -2686,7 +2701,8 @@ static void intel_disable_dp(struct intel_encoder *encoder,
> 
> It's not clear why the DDI counterpart is missing.

Because I forgot we have the same code in two places ;) v2 coming up...

> 
> >  	 * ensure that we have vdd while we switch off the panel. */
> >  	intel_edp_panel_vdd_on(intel_dp);
> >  	intel_edp_backlight_off(old_conn_state);
> > -	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_OFF);
> > +	if (!downstream_hpd_needs_d0(intel_dp))
> > +		intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_OFF);
> >  	intel_edp_panel_off(intel_dp);
> >  }
> >  

-- 
Ville Syrjälä
Intel OTC
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