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

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

On Tue, 25 Aug 2015, Sivakumar Thulasimani <sivakumar.thulasimani@intel.com> 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.

Having to write "also" in a commit message is a good hint to stop and
think about whether that should be a separate patch. Maybe it should be,
here too?

BR,
Jani.

>
> 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;
> -
>  	/* 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
>

-- 
Jani Nikula, Intel Open Source Technology Center
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