[4.2.y-ckt stable] Patch "drm/i915: Bail out of pipe config compute loop on LPT" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    drm/i915: Bail out of pipe config compute loop on LPT

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt11.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From c133e353a3e28edca2896f07192f6ca14b8728e8 Mon Sep 17 00:00:00 2001
From: Daniel Vetter <daniel.vetter at ffwll.ch>
Date: Tue, 3 May 2016 10:33:01 +0200
Subject: drm/i915: Bail out of pipe config compute loop on LPT

commit 2700818ac9f935d8590715eecd7e8cadbca552b6 upstream.

LPT is pch, so might run into the fdi bandwidth constraint (especially
since it has only 2 lanes). But right now we just force pipe_bpp back
to 24, resulting in a nice loop (which we bail out with a loud
WARN_ON). Fix this.

Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
References: https://bugs.freedesktop.org/show_bug.cgi?id=93477
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
Tested-by: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1462264381-7573-1-git-send-email-daniel.vetter@ffwll.ch
(cherry picked from commit f58a1acc7e4a1f37d26124ce4c875c647fbcc61f)
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpu/drm/i915/intel_crt.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 521af2c..1b34f00 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -320,8 +320,14 @@ static bool intel_crt_compute_config(struct intel_encoder *encoder,
 		pipe_config->has_pch_encoder = true;

 	/* LPT FDI RX only supports 8bpc. */
-	if (HAS_PCH_LPT(dev))
+	if (HAS_PCH_LPT(dev)) {
+		if (pipe_config->bw_constrained && pipe_config->pipe_bpp < 24) {
+			DRM_DEBUG_KMS("LPT only supports 24bpp\n");
+			return false;
+		}
+
 		pipe_config->pipe_bpp = 24;
+	}

 	/* FDI must always be 2.7 GHz */
 	if (HAS_DDI(dev)) {
--
2.7.4