Re: Valid DP connection without EDID?

[Adam Jackson <ajax@redhat.com>]

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On Tue, 2012-09-18 at 13:01 +0200, Takashi Iwai wrote:

> > I started a patch series for this a bit ago, I'll send it on
> > momentarily.
> 
> Thanks!  I evaluated it now (with a typo fix suggested by Jani).
> Unfortunately, it doesn't improve the situation.
> 
> The fetch of downstream ports succeeds, and it gets 0x09.  So, this
> indicates again it's a VGA downstream port.  But that's all, so far.
> The 0x09 is reported no matter whether the VGA cable is plugged or
> not, so this can't be used as the detection of the downstream port
> plug state.

Sorry, there's a bug in the patch.  link_configuration[0] is not
DP_SINK_COUNT, I have no idea why I thought it was.  Try this on top of
the series:

===
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 9809c53..b6b9a18 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -2098,15 +2098,22 @@ intel_dp_detect_dpcd(struct intel_dp *intel_dp)
 
        if (!intel_dp_get_dpcd(intel_dp))
                return connector_status_disconnected;
-       
+
        /* if there's no downstream port, we're done */
        if (!(dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT))
                return connector_status_connected;
 
        /* If we're HPD-aware, SINK_COUNT changes dynamically */
        hpd = !!(intel_dp->downstream_ports[0] & DP_DS_PORT_HPD);
-       if (hpd && (intel_dp->link_configuration[0] & DP_SINK_COUNT_MASK))
-               return connector_status_connected;
+       if (hpd) {
+               uint8_t sink_count;
+               if (!intel_dp_aux_native_read_retry(intel_dp, DP_SINK_COUNT,
+                                                   &sink_count, 1))
+                       return connector_status_unknown;
+               sink_count &= DP_SINK_COUNT_MASK;
+               return sink_count ? connector_status_connected
+                                 : connector_status_disconnected;
+       }
 
        /* If no HPD, poke DDC gently */
        if (drm_probe_ddc(&intel_dp->adapter))
===

If that doesn't work then the HPD-capable bit is useless - or if we're
lucky just needs quirking by branch OUI - and we should just fall
through to the drm_probe_ddc() path.  What is the branch OUI, anyway?

There's a third possibility, which is that HPD does work but that we're
not doing enough to enable it.  The DP 1.1a spec has a non-normative
appendix describing one way a device could go about doing that as an
optional feature, but the method described does not match how we're
currently handling sink-specific IRQs.  I have no idea what the 1.2 spec
says on this point though.

- ajax

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