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From f0b604bc081eb78737212cb27f2c454a9e6928d6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <>
Date: Fri, 20 Sep 2013 10:14:23 +0300
Subject: drm/i915: Fix unclaimed register access due to delayed VGA memory
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VGA registers live inside the power well on HSW, so in order to write
the VGA MSR register we need the power well to be on.
We really must write to the register to properly clear the
VGA_MSR_MEM_EN enable bit, even if all VGA registers get zeroed when
the power well is down. It seems that the implicit zeroing done by
the power well is not enough to propagate the VGA_MSR_MEM_EN bit to
whomever is actually responsible for the memory decode ranges.
If we leave VGA memory decode enabled, and then turn off the power well,
all VGA memory reads will return zeroes. But if we first disable VGA
memory deocde and then turn off the power well, VGA memory reads
return all ones, indicating that the access wasn't claimed by anyone.
For the vga arbiter to function correctly the IGD must not claim the
VGA memory accesses.
Previously we were doing the VGA_MSR register access while the power well
was excplicitly powered up during driver init. But ever since
commit 6e1b4fdad5157bb9e88777d525704aba24389bee
Author: Ville Syrjälä <>
Date: Thu Sep 5 20:40:52 2013 +0300
drm/i915: Delay disabling of VGA memory until vgacon->fbcon handoff is done
we delay the VGA memory disable until fbcon has initialized, and so
there's a possibility that the power well got turned off during the
fbcon modeset. Also vgacon_save_screen() will need the power well to be
on to be able to read the VGA memory.
So immediately after enabling the power well during init grab a refence
for VGA purposes, and after all the VGA handling is done, release it.
v2: Add intel_display_power_put() for the num_pipes==0 case
Signed-off-by: Ville Syrjälä <>
Reviewed-by: Paulo Zanoni <>
[danvet: Fix up the patch wiggle screw-up that I've done and which
Paulo catched. Also polish spelling in the patch headline.]
Signed-off-by: Daniel Vetter <>
(cherry picked from commit ce352550327b394f3072a07c9cd9d27af9276f15)
Signed-off-by: Darren Hart <>
drivers/gpu/drm/i915/i915_dma.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1334,13 +1334,18 @@ static int i915_load_modeset_init(struct
+ /* Keep VGA alive until i915_disable_vga_mem() */
+ intel_display_power_get(dev, POWER_DOMAIN_VGA);
/* Always safe in the mode setting case. */
/* FIXME: do pre/post-mode set stuff in core KMS code */
dev->vblank_disable_allowed = 1;
- if (INTEL_INFO(dev)->num_pipes == 0)
+ if (INTEL_INFO(dev)->num_pipes == 0) {
+ intel_display_power_put(dev, POWER_DOMAIN_VGA);
return 0;
+ }
ret = intel_fbdev_init(dev);
if (ret)
@@ -1366,6 +1371,7 @@ static int i915_load_modeset_init(struct
* vgacon_save_screen() works during the handover.
+ intel_display_power_put(dev, POWER_DOMAIN_VGA);
/* Only enable hotplug handling once the fbdev is fully set up. */
dev_priv->enable_hotplug_processing = true;