Re: [PATCH] drm/i915: Don't trust the DP_DETECT bit for eDP ports on CHV

[Damien Lespiau <damien.lespiau@intel.com>]

On Thu, Oct 09, 2014 at 07:37:15PM +0300, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> On CHV the display DDC pins may be muxed to an alternate function if
> there's no need for DDC on a specific port, which is the case for eDP
> ports since there's no way to plug in a DP++ HDMI dongle.
> 
> This causes problems when trying to determine if the port is present
> since the the DP_DETECTED bit is the latched state of the DDC SDA pin
> at boot. If the DDC pins are muxed to an alternate function the bit
> may indicate that the port isn't present.
> 
> To work around this look at the VBT as well as the DP_DETECTED bit
> to determine if we should attempt registering an eDP port. Do this
> only for ports B and C since port D doesn't support eDP (no PPS/BLC).
> 
> In theory someone could also wire up a normal DP port w/o DDC lines.
> That would just mean that simple DP++ HDMI dongles wouldn't work
> on such a port. With this change we would still fail to register
> such DP ports. But let's hope no one wires their board in such a way,
> and if they do we can extend the VBT checks to cover normal DP ports
> as well.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=84265
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>

-- 
Damien

> ---
>  drivers/gpu/drm/i915/intel_display.c | 33 +++++++++++++++++++++------------
>  1 file changed, 21 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index b5476dc..d6fc469 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -12280,27 +12280,36 @@ static void intel_setup_outputs(struct drm_device *dev)
>  		if (I915_READ(PCH_DP_D) & DP_DETECTED)
>  			intel_dp_init(dev, PCH_DP_D, PORT_D);
>  	} else if (IS_VALLEYVIEW(dev)) {
> -		if (I915_READ(VLV_DISPLAY_BASE + GEN4_HDMIB) & SDVO_DETECTED) {
> +		/*
> +		 * The DP_DETECTED bit is the latched state of the DDC
> +		 * SDA pin at boot. However since eDP doesn't require DDC
> +		 * (no way to plug in a DP->HDMI dongle) the DDC pins for
> +		 * eDP ports may have been muxed to an alternate function.
> +		 * Thus we can't rely on the DP_DETECTED bit alone to detect
> +		 * eDP ports. Consult the VBT as well as DP_DETECTED to
> +		 * detect eDP ports.
> +		 */
> +		if (I915_READ(VLV_DISPLAY_BASE + GEN4_HDMIB) & SDVO_DETECTED)
>  			intel_hdmi_init(dev, VLV_DISPLAY_BASE + GEN4_HDMIB,
>  					PORT_B);
> -			if (I915_READ(VLV_DISPLAY_BASE + DP_B) & DP_DETECTED)
> -				intel_dp_init(dev, VLV_DISPLAY_BASE + DP_B, PORT_B);
> -		}
> +		if (I915_READ(VLV_DISPLAY_BASE + DP_B) & DP_DETECTED ||
> +		    intel_dp_is_edp(dev, PORT_B))
> +			intel_dp_init(dev, VLV_DISPLAY_BASE + DP_B, PORT_B);
>  
> -		if (I915_READ(VLV_DISPLAY_BASE + GEN4_HDMIC) & SDVO_DETECTED) {
> +		if (I915_READ(VLV_DISPLAY_BASE + GEN4_HDMIC) & SDVO_DETECTED)
>  			intel_hdmi_init(dev, VLV_DISPLAY_BASE + GEN4_HDMIC,
>  					PORT_C);
> -			if (I915_READ(VLV_DISPLAY_BASE + DP_C) & DP_DETECTED)
> -				intel_dp_init(dev, VLV_DISPLAY_BASE + DP_C, PORT_C);
> -		}
> +		if (I915_READ(VLV_DISPLAY_BASE + DP_C) & DP_DETECTED ||
> +		    intel_dp_is_edp(dev, PORT_C))
> +			intel_dp_init(dev, VLV_DISPLAY_BASE + DP_C, PORT_C);
>  
>  		if (IS_CHERRYVIEW(dev)) {
> -			if (I915_READ(VLV_DISPLAY_BASE + CHV_HDMID) & SDVO_DETECTED) {
> +			if (I915_READ(VLV_DISPLAY_BASE + CHV_HDMID) & SDVO_DETECTED)
>  				intel_hdmi_init(dev, VLV_DISPLAY_BASE + CHV_HDMID,
>  						PORT_D);
> -				if (I915_READ(VLV_DISPLAY_BASE + DP_D) & DP_DETECTED)
> -					intel_dp_init(dev, VLV_DISPLAY_BASE + DP_D, PORT_D);
> -			}
> +			/* eDP not supported on port D, so don't check VBT */
> +			if (I915_READ(VLV_DISPLAY_BASE + DP_D) & DP_DETECTED)
> +				intel_dp_init(dev, VLV_DISPLAY_BASE + DP_D, PORT_D);
>  		}
>  
>  		intel_dsi_init(dev);
> -- 
> 2.0.4
> 
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