[Bug 87171] 3.18: i855GM KMS regression

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=87171

--- Comment #12 from Bruno <bonbons67 at internet.lu> ---
The VGACNTRL value as saved early on:
  0x6104008e

That has both VGA_2X_MODE and VGA_PIPE_B_SELECT bits set (plus a whole bunch of
bits on the less significant bytes).

With patch 69769f9a422bfc62e17399da3590c5e31ac37f24 included VGACNTRL would be
set to 0xe104008e.
If I mask VGA_2X_MODE I get proper output on my 1440x1050 LVDS display.

Thus the following patch on top of 3.18 fixes the issue for me (as an
alternative to reverting commit 69769f9a42):
diff --git a/drivers/gpu/drm/i915/intel_display.c
b/drivers/gpu/drm/i915/intel_display.c
index 9cb5c95..fc4e16d 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12937,7 +12937,7 @@ static void i915_disable_vga(struct drm_device *dev)
      * Fujitsu-Siemens Lifebook S6010 (830) has problems resuming
      * from S3 without preserving (some of?) the other bits.
      */
-    I915_WRITE(vga_reg, dev_priv->bios_vgacntr | VGA_DISP_DISABLE);
+    I915_WRITE(vga_reg, (dev_priv->bios_vgacntr | VGA_DISP_DISABLE) &
+                        ~VGA_2X_MODE);
     POSTING_READ(vga_reg);
 }

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