Re: [PATCH 1/3] drm/i915: read sink_count dpcd always

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

On Tue, Aug 25, 2015 at 05:20:36PM +0530, Sivakumar Thulasimani wrote:
> From: "Thulasimani,Sivakumar" <sivakumar.thulasimani@intel.com>
> 
> This patch reads sink_count dpcd always and removes its
> read operation based on values in downstream port dpcd. Also
> we should read it irrespective of current status of sink.
> 
> SINK_COUNT dpcd is not dependent on DOWNSTREAM_PORT_PRESENT dpcd.
> SINK_COUNT denotes if a display is attached, while
> DOWNSTREAM_PORT_PRESET indicates how many ports are available
> in the dongle where display can be attached. so it is possible
> for sink count to change irrespective of value in downstream
> port dpcd.
> 
> Here is a table of possible values and scenarios
> 
> sink_count	downstream_port
> 		present
> 0		0		no display is attached
> 0		1		dongle is connected without display
> 1		0		display connected directly
> 1		1		display connected through dongle
> 
> Signed-off-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c |   33 ++++++++++++++-------------------
>  1 file changed, 14 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 8a66a44..9e4e27d 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -3898,6 +3898,7 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
>  	struct drm_device *dev = dig_port->base.base.dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	uint8_t rev;
> +	uint8_t reg;
>  
>  	if (intel_dp_dpcd_read_wake(&intel_dp->aux, 0x000, intel_dp->dpcd,
>  				    sizeof(intel_dp->dpcd)) < 0)
> @@ -3908,6 +3909,13 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
>  	if (intel_dp->dpcd[DP_DPCD_REV] == 0)
>  		return false; /* DPCD not present */
>  
> +	if (intel_dp_dpcd_read_wake(&intel_dp->aux, DP_SINK_COUNT,
> +					    &reg, 1) < 0)
> +			return false;
> +
> +	if (!DP_GET_SINK_COUNT(reg))
> +		return false;
> +
>  	/* Check if the panel supports PSR */
>  	memset(intel_dp->psr_dpcd, 0, sizeof(intel_dp->psr_dpcd));
>  	if (is_edp(intel_dp)) {
> @@ -4374,12 +4382,6 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
>  
>  	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
>  
> -	if (!intel_encoder->base.crtc)
> -		return;
> -
> -	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
> -		return;
> -

I don't like trying to overload intel_dp_check_link_status() to do other
stuff besides link retraining. The sink irq stuff already snuck in
somehow, but I think we should pull it out and try to make the function
names match what they do.

The entire DP hpd locking also needs more though. We now grab the
connection_mutex for the retraining to prevent racing against modeset,
but it doesn't prevent racing against ->detect(). And for MST we take
no locks whatsoever, even for the retraining (I have a patch for that
that I'll send out soon).

>  	/* Try to read receiver status if the link appears to be up */
>  	if (!intel_dp_get_link_status(intel_dp, link_status)) {
>  		return;
> @@ -4390,6 +4392,12 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
>  		return;
>  	}
>  
> +	if (!intel_encoder->base.crtc)
> +		return;
> +
> +	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
> +		return;
> +
>  	/* Try to read the source of the interrupt */
>  	if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11 &&
>  	    intel_dp_get_sink_irq(intel_dp, &sink_irq_vector)) {
> @@ -4427,19 +4435,6 @@ intel_dp_detect_dpcd(struct intel_dp *intel_dp)
>  	if (!(dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT))
>  		return connector_status_connected;
>  
> -	/* If we're HPD-aware, SINK_COUNT changes dynamically */
> -	if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11 &&
> -	    intel_dp->downstream_ports[0] & DP_DS_PORT_HPD) {
> -		uint8_t reg;
> -
> -		if (intel_dp_dpcd_read_wake(&intel_dp->aux, DP_SINK_COUNT,
> -					    &reg, 1) < 0)
> -			return connector_status_unknown;
> -
> -		return DP_GET_SINK_COUNT(reg) ? connector_status_connected
> -					      : connector_status_disconnected;
> -	}
> -
>  	/* If no HPD, poke DDC gently */
>  	if (drm_probe_ddc(&intel_dp->aux.ddc))
>  		return connector_status_connected;
> -- 
> 1.7.9.5

-- 
Ville Syrjälä
Intel OTC
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