Patch "drm/i915: Assume non-DP++ port if dvo_port is HDMI and there's no AUX ch specified in the VBT" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

drm/i915: Assume non-DP++ port if dvo_port is HDMI and there's no AUX ch specified in the VBT

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-i915-assume-non-dp-port-if-dvo_port-is-hdmi-and-there-s-no-aux-ch-specified-in-the-vbt.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <[email protected]>
Date: Fri, 11 Nov 2016 19:14:24 +0200
Subject: drm/i915: Assume non-DP++ port if dvo_port is HDMI and there's no AUX ch specified in the VBT
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From: Ville Syrjälä <[email protected]>

commit bc9db5ad3253c8e17969bd802c47b73e63f125ab upstream.

My heuristic for detecting type 1 DVI DP++ adaptors based on the VBT port information apparently didn't survive the reality of buggy VBTs. In this particular case we have a machine with a natice HDMI port, but the VBT tells us it's a DP++ port based on its capabilities.

The dvo_port information in VBT does claim that we're dealing with a HDMI port though, but we have other machines which do the same even when they actually have DP++ ports. So that piece of information alone isn't sufficient to tell the two apart.

After staring at a bunch of VBTs from various machines, I have to conclude that the only other semi-reliable clue we can use is the presence of the AUX channel in the VBT. On this particular machine AUX channel is specified as zero, whereas on some of the other machines which listed the DP++ port as HDMI have a non-zero AUX channel.

I've also seen VBTs which have dvo_port a DP but have a zero AUX channel. I believe those we need to treat as DP ports, so we'll limit the AUX channel check to just the cases where dvo_port is HDMI.

If we encounter any more serious failures with this heuristic I think we'll have to have to throw it out entirely. But that could mean that there is a risk of type 1 DVI dongle users getting greeted by a black screen, so I'd rather not go there unless absolutely necessary.

v2: Remove the duplicate PORT_A check (Daniel)
Fix some typos in the commit message

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97994

---
 drivers/gpu/drm/i915/intel_bios.c     |   30 ++++++++++++++++++++++--------
 drivers/gpu/drm/i915/intel_vbt_defs.h |    3 ++-
 2 files changed, 24 insertions(+), 9 deletions(-)

@@ -1143,7 +1143,7 @@ static void parse_ddi_port(struct drm_i9
 	if (!child)
 		return;
 
-	aux_channel = child->raw[25];
+	aux_channel = child->common.aux_channel;
 	ddc_pin = child->common.ddc_pin;
 
 	is_dvi = child->common.device_type & DEVICE_TYPE_TMDS_DVI_SIGNALING;

@@ -1673,7 +1673,8 @@ bool intel_bios_is_port_edp(struct drm_i
 	return false;
 }
 
-bool intel_bios_is_port_dp_dual_mode(struct drm_i915_private *dev_priv, enum port port)
+static bool child_dev_is_dp_dual_mode(const union child_device_config *p_child,
+				      enum port port)
 {
 	static const struct {
 		u16 dp, hdmi;

@@ -1687,22 +1688,35 @@ bool intel_bios_is_port_dp_dual_mode(str
 		[PORT_D] = { DVO_PORT_DPD, DVO_PORT_HDMID, },
 		[PORT_E] = { DVO_PORT_DPE, DVO_PORT_HDMIE, },
 	};
-	int i;
 
 	if (port == PORT_A || port >= ARRAY_SIZE(port_mapping))
 		return false;
 
-	if (!dev_priv->vbt.child_dev_num)
+	if ((p_child->common.device_type & DEVICE_TYPE_DP_DUAL_MODE_BITS) !=
+	    (DEVICE_TYPE_DP_DUAL_MODE & DEVICE_TYPE_DP_DUAL_MODE_BITS))
 		return false;
 
+	if (p_child->common.dvo_port == port_mapping[port].dp)
+		return true;
+
+	/* Only accept a HDMI dvo_port as DP++ if it has an AUX channel */
+	if (p_child->common.dvo_port == port_mapping[port].hdmi &&
+	    p_child->common.aux_channel != 0)
+		return true;
+
+	return false;
+}
+
+bool intel_bios_is_port_dp_dual_mode(struct drm_i915_private *dev_priv,
+				     enum port port)
+{
+	int i;
+
 	for (i = 0; i < dev_priv->vbt.child_dev_num; i++) {
 		const union child_device_config *p_child =
 			&dev_priv->vbt.child_dev[i];
 
-		if ((p_child->common.dvo_port == port_mapping[port].dp ||
-		     p_child->common.dvo_port == port_mapping[port].hdmi) &&
-		    (p_child->common.device_type & DEVICE_TYPE_DP_DUAL_MODE_BITS) ==
-		    (DEVICE_TYPE_DP_DUAL_MODE & DEVICE_TYPE_DP_DUAL_MODE_BITS))
+		if (child_dev_is_dp_dual_mode(p_child, port))
 			return true;
 	}
 

@@ -280,7 +280,8 @@ struct common_child_dev_config {
 	u8 dp_support:1;
 	u8 tmds_support:1;
 	u8 support_reserved:5;
-	u8 not_common3[12];
+	u8 aux_channel;
+	u8 not_common3[11];
 	u8 iboost_level;
 } __packed;
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/drm-i915-refresh-that-status-of-mst-capable-connectors-in-detect.patch queue-4.8/drm-i915-assume-non-dp-port-if-dvo_port-is-hdmi-and-there-s-no-aux-ch-specified-in-the-vbt.patch