Re: [PATCH 2/2] drm/i915: Ignore long hpds on eDP ports

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

On Thu, 16 Oct 2014, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Turning vdd on/off can generate a long hpd pulse on eDP ports. In order
> to handle hpd we would need to turn on vdd to perform aux transfers.
> This would lead to an endless cycle of
> "vdd off -> long hpd -> vdd on -> detect -> vdd off -> ..."
>
> So ignore long hpd pulses on eDP ports. eDP panels should be physically
> tied to the machine anyway so they should not actually disappear and
> thus don't need long hpd handling. Short hpds are still needed for link
> re-train and whatnot so we can't just turn off the hpd interrupt
> entirely for eDP ports. Perhaps we could turn it off whenever the panel
> is disabled, but just ignoring the long hpd seems sufficient.

Did you test this with my short vs. long hpd fix applied?

In any case, makes sense,

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





>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index f07f02c..4455009 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -4611,6 +4611,18 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
>  	if (intel_dig_port->base.type != INTEL_OUTPUT_EDP)
>  		intel_dig_port->base.type = INTEL_OUTPUT_DISPLAYPORT;
>  
> +	if (long_hpd && intel_dig_port->base.type == INTEL_OUTPUT_EDP) {
> +		/*
> +		 * vdd off can generate a long pulse on eDP which
> +		 * would require vdd on to handle it, and thus we
> +		 * would end up in an endless cycle of
> +		 * "vdd off -> long hpd -> vdd on -> detect -> vdd off -> ..."
> +		 */
> +		DRM_DEBUG_KMS("ignoring long hpd on eDP port %c\n",
> +			      port_name(intel_dig_port->port));
> +		return false;
> +	}
> +
>  	DRM_DEBUG_KMS("got hpd irq on port %c - %s\n",
>  		      port_name(intel_dig_port->port),
>  		      long_hpd ? "long" : "short");
> -- 
> 2.0.4
>
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-- 
Jani Nikula, Intel Open Source Technology Center
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