[3.19.y-ckt stable] Patch "drm/i915: Preserve SSC earlier" has been added to staging queue

[Kamal Mostafa]

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

    drm/i915: Preserve SSC earlier

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt8.

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

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 89960d50dd4b65d1090f99e762b4b83c188cfb4e Mon Sep 17 00:00:00 2001
From: Lukas Wunner <lukas at wunner.de>
Date: Wed, 15 Jul 2015 13:57:35 +0200
Subject: drm/i915: Preserve SSC earlier

commit 69f92f67b68ab7028ffe15f0eea76b59f8859383 upstream.

Commit 92122789b2d6 ("drm/i915: preserve SSC if previously set v3")
added code to intel_modeset_gem_init to override the SSC status read
from VBT with the SSC status set by BIOS.

However, intel_modeset_gem_init is invoked *after* intel_modeset_init,
which calls intel_setup_outputs, which *modifies* SSC status by way of
intel_init_pch_refclk. So unlike advertised, intel_modeset_gem_init
doesn't preserve the SSC status set by BIOS but whatever
intel_init_pch_refclk decided on.

This is a problem on dual gpu laptops such as the MacBook Pro which
require either a handler to switch DDC lines, or the discrete gpu
to proxy DDC/AUX communication: Both the handler and the discrete
gpu may initialize after the i915 driver, and consequently, an LVDS
connector may initially seem disconnected and the SSC therefore
is disabled by intel_init_pch_refclk, but on reprobe the connector
may turn out to be connected and the SSC must then be enabled.

Due to 92122789b2d6 however, the SSC is not enabled on reprobe since
it is assumed BIOS disabled it while in fact it was disabled by
intel_init_pch_refclk.

Also, because the SSC status is preserved so late, the preserved value
only ever gets used on resume but not on panel initialization:
intel_modeset_init calls intel_init_display which indirectly calls
intel_panel_use_ssc via multiple subroutines, *before* the BIOS value
overrides the VBT value in intel_modeset_gem_init (intel_panel_use_ssc
is the sole user of dev_priv->vbt.lvds_use_ssc).

Fix this by moving the code introduced by 92122789b2d6 from
intel_modeset_gem_init to intel_modeset_init before the invocation
of intel_setup_outputs and intel_init_display.

Add a DRM_DEBUG_KMS as suggested way back by Jani:
http://lists.freedesktop.org/archives/intel-gfx/2014-June/046666.html

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88861
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115
Tested-by: Paul Hordiienko <pvt.gord at gmail.com>
    [MBP  6,2 2010  intel ILK + nvidia GT216  pre-retina]
Tested-by: William Brown <william at blackhats.net.au>
    [MBP  8,2 2011  intel SNB + amd turks     pre-retina]
Tested-by: Lukas Wunner <lukas at wunner.de>
    [MBP  9,1 2012  intel IVB + nvidia GK107  pre-retina]
Tested-by: Bruno Bierbaumer <bruno at bierbaumer.net>
    [MBP 11,3 2013  intel HSW + nvidia GK107  retina -- work in progress]
Fixes: 92122789b2d6 ("drm/i915: preserve SSC if previously set v3")
Signed-off-by: Lukas Wunner <lukas at wunner.de>
Reviewed-by: Jesse Barnes <jbarnes at virtuousgeek.org>
Signed-off-by: Jani Nikula <jani.nikula at intel.com>

Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpu/drm/i915/intel_display.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 791b00e..ada0210 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13104,6 +13104,24 @@ void intel_modeset_init(struct drm_device *dev)
 	if (INTEL_INFO(dev)->num_pipes == 0)
 		return;

+	/*
+	 * There may be no VBT; and if the BIOS enabled SSC we can
+	 * just keep using it to avoid unnecessary flicker.  Whereas if the
+	 * BIOS isn't using it, don't assume it will work even if the VBT
+	 * indicates as much.
+	 */
+	if (HAS_PCH_IBX(dev) || HAS_PCH_CPT(dev)) {
+		bool bios_lvds_use_ssc = !!(I915_READ(PCH_DREF_CONTROL) &
+					    DREF_SSC1_ENABLE);
+
+		if (dev_priv->vbt.lvds_use_ssc != bios_lvds_use_ssc) {
+			DRM_DEBUG_KMS("SSC %sabled by BIOS, overriding VBT which says %sabled\n",
+				     bios_lvds_use_ssc ? "en" : "dis",
+				     dev_priv->vbt.lvds_use_ssc ? "en" : "dis");
+			dev_priv->vbt.lvds_use_ssc = bios_lvds_use_ssc;
+		}
+	}
+
 	intel_init_display(dev);
 	intel_init_audio(dev);

@@ -13590,7 +13608,6 @@ void intel_modeset_setup_hw_state(struct drm_device *dev,

 void intel_modeset_gem_init(struct drm_device *dev)
 {
-	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_crtc *c;
 	struct drm_i915_gem_object *obj;

@@ -13598,16 +13615,6 @@ void intel_modeset_gem_init(struct drm_device *dev)
 	intel_init_gt_powersave(dev);
 	mutex_unlock(&dev->struct_mutex);

-	/*
-	 * There may be no VBT; and if the BIOS enabled SSC we can
-	 * just keep using it to avoid unnecessary flicker.  Whereas if the
-	 * BIOS isn't using it, don't assume it will work even if the VBT
-	 * indicates as much.
-	 */
-	if (HAS_PCH_IBX(dev) || HAS_PCH_CPT(dev))
-		dev_priv->vbt.lvds_use_ssc = !!(I915_READ(PCH_DREF_CONTROL) &
-						DREF_SSC1_ENABLE);
-
 	intel_modeset_init_hw(dev);

 	intel_setup_overlay(dev);
--
1.9.1