Re: [PATCH v2] drm/i915: Improve DP downstream HPD handling

[Jani Nikula <jani.nikula@linux.intel.com>]

On Fri, 27 Oct 2017, Ville Syrjala <ville.syrjala@linux.intel.com> 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.
>
> v2: Deal with DDI as well by moving the check into
>     intel_dp_sink_dpms() (Dhinakaran)
>
> Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> 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>

Reviewed-by: Jani Nikula <jani.nikula@intel.com>


> ---
>  drivers/gpu/drm/i915/intel_dp.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index aa75f55eeb61..59169a4dc9d3 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -2505,6 +2505,21 @@ static void ironlake_edp_pll_off(struct intel_dp *intel_dp)
>  	udelay(200);
>  }
>  
> +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;
> +}
> +
>  /* If the sink supports it, try to set the power state appropriately */
>  void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode)
>  {
> @@ -2515,6 +2530,9 @@ void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode)
>  		return;
>  
>  	if (mode != DRM_MODE_DPMS_ON) {
> +		if (downstream_hpd_needs_d0(intel_dp))
> +			return;
> +
>  		ret = drm_dp_dpcd_writeb(&intel_dp->aux, DP_SET_POWER,
>  					 DP_SET_POWER_D3);
>  	} else {

-- 
Jani Nikula, Intel Open Source Technology Center
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