[Intel-gfx] [PATCH] drm/i915: Improve DP downstream HPD handling

[Pandiyan, Dhinakaran]

On Thu, 2017-10-26 at 22:41 +0300, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala at 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 at infradead.org>
> Cc: Imre Deak <imre.deak at intel.com>
> Cc: Pablo <pablodebiase at 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 at 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.

>  	 * 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);
>  }
>