[Intel-gfx] [PATCH 2/4] drm/i915: read sink_count dpcd always

[Jani Nikula]

On Thu, 27 Aug 2015, Sivakumar Thulasimani <sivakumar.thulasimani at intel.com> wrote:
> From: "Thulasimani,Sivakumar" <sivakumar.thulasimani at intel.com>
>
> This patch reads sink_count dpcd always and removes its
> read operation based on values in downstream port dpcd.
>
> 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.

This makes sense.

I'm scared this may break something, if there are displays/adapters out
there that don't set sink count properly. I guess only one way to find
out... And this might actually fix something else.

> 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

Do you think you handle this last case properly now? Previously we'd
return with "connected" at the sink count check, but now we'll go for
the "pke ddc gently" phase.

See below.

>
> v2: moved out crtc enabled checks to prior patch(Jani)
>
> Signed-off-by: Sivakumar Thulasimani <sivakumar.thulasimani at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c |   21 ++++++++-------------
>  1 file changed, 8 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 76561e0..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)) {
> @@ -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;
> -	}
> -

Why do we proceed here if we know that we have sink count > 0 and we
have a downstream port present? Admittedly I'm not sure I understand (or
remember) why we had this logic in the first place...

BR,
Jani.

>  	/* 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