Patch "drm/radeon: Fix eDP for single-display iMac10,1 (v2)" has been added to the 4.9-stable tree

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

drm/radeon: Fix eDP for single-display iMac10,1 (v2)

to the 4.9-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-radeon-fix-edp-for-single-display-imac10-1-v2.patch

and it can be found in the queue-4.9 subdirectory.

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

From: Mario Kleiner <[email protected]>
Date: Fri, 7 Jul 2017 04:57:04 +0200
Subject: drm/radeon: Fix eDP for single-display iMac10,1 (v2)
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From: Mario Kleiner <[email protected]>

commit 564d8a2cf3abf16575af48bdc3e86e92ee8a617d upstream.

The late 2009, 27 inch Apple iMac10,1 has an internal eDP display and an external Mini- Displayport output, driven by a DCE-3.2, RV730 Radeon Mobility HD-4670.

The machine worked fine in a dual-display setup with eDP panel + externally connected HDMI
or DVI-D digital display sink, connected via MiniDP to DVI or HDMI adapter.

However, booting the machine single-display with only eDP panel results in a completely black display - even backlight powering off, as soon as the radeon modesetting driver loads.

This patch fixes the single dispay eDP case by assigning encoders based on dig->linkb, similar to DCE-4+. While this should not be generally necessary (Alex: "...atom on normal boards should be able to handle any mapping."), Apple seems to use some special routing here.

One remaining problem not solved by this patch is that an external Minidisplayport->DP sink does still not work on iMac10,1, whereas external DVI and HDMI sinks continue to work.

The problem affects at least all tested kernels since Linux 3.13 - didn't test earlier kernels, so backporting to stable probably makes sense.

v2: With the original patch from 2016, Alex was worried it
will break other DCE3.2 systems. Use dmi_match() to apply this special encoder assignment only for the Apple iMac 10,1 from late 2009.

---
 drivers/gpu/drm/radeon/atombios_encoders.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

@@ -30,6 +30,7 @@
 #include "radeon_audio.h"
 #include "atom.h"
 #include <linux/backlight.h>
+#include <linux/dmi.h>
 
 extern int atom_debug;
 

@@ -2183,9 +2184,17 @@ int radeon_atom_pick_dig_encoder(struct
 		goto assigned;
 	}
 
-	/* on DCE32 and encoder can driver any block so just crtc id */
+	/*
+	 * On DCE32 any encoder can drive any block so usually just use crtc id,
+	 * but Apple thinks different at least on iMac10,1, so there use linkb,
+	 * otherwise the internal eDP panel will stay dark.
+	 */
 	if (ASIC_IS_DCE32(rdev)) {
-		enc_idx = radeon_crtc->crtc_id;
+		if (dmi_match(DMI_PRODUCT_NAME, "iMac10,1"))
+			enc_idx = (dig->linkb) ? 1 : 0;
+		else
+			enc_idx = radeon_crtc->crtc_id;
+
 		goto assigned;
 	}
 

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

queue-4.9/drm-radeon-fix-edp-for-single-display-imac10-1-v2.patch