[Intel-gfx] Fwd: [PATCH] CHROMIUM: i915: Added default LVDS options for the no-VBT case

Simon Que sque at chromium.org
Thu Sep 23 21:20:02 CEST 2010

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Please see below, thanks.


---------- Forwarded message ----------
From:  <intel-gfx-owner at lists.freedesktop.org>
Date: Thu, Sep 23, 2010 at 12:10 PM
Subject: [PATCH] CHROMIUM: i915: Added default LVDS options for the no-VBT case
To: sque at chromium.org

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---------- Forwarded message ----------
From: Simon Que <sque at chromium.org>
To: Chris Wilson <chris at chris-wilson.co.uk>, Jesse Barnes
<jbarnes at virtuousgeek.org>, Eric Anholt <eric at anholt.net>,
intel-gfx at lists.freedesktop.org
Date: Thu, 23 Sep 2010 12:10:49 -0700
Subject: [PATCH] CHROMIUM: i915: Added default LVDS options for the no-VBT case

Here is a patch that sets default LVDS values for the i915 video
driver when there is no Video BIOS Table (VBT) found.

Currently, intel_bios.c in the i915 driver attempts to find the VBT.
- If the VBT is found, it will parse the VBT for each section.  The
parse functions set default values for each section in case that
section is missing from the VBT.
- If the VBT is not found, it exits without setting anything.

There are no default settings for the second case, where the VBT is
not found.  This patch will add a function that is called only in the
case of VBT not being found.  The function will set some default
values for the video driver.

Currently the only thing that is being set by this function is the
dither bit.  More could be added in the future.  The motivation is
that our hardware does not have a VBT, but the dither bit needs to be
set for the display to work properly.  We expect that the case of not
having a VBT will be rare on other systems.

Please provide your comments and feedback.



Subject: [PATCH] CHROMIUM: i915: Added default LVDS options for the no-VBT case
Added a function that sets the LVDS values to default settings (currently only
dither bit) when there is no VBT (video BIOS table) found.
Signed-off-by: Simon Que <sque at chromium.org>
TEST=Splash screen looks dithered upon boot.
Change-Id: If19c763824ee938ad107f655d8d94c65e39cfa56
 drivers/gpu/drm/Kconfig |    9 +++++++++
 drivers/gpu/drm/i915/intel_bios.c |   10 ++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_bios.c
index 70c9d4b..ad76f30 100644
--- a/drivers/gpu/drm/i915/intel_bios.c
+++ b/drivers/gpu/drm/i915/intel_bios.c
@@ -501,6 +501,15 @@ parse_device_mapping(struct drm_i915_private *dev_priv,
+static void
+get_no_vbt_default_settings(struct drm_i915_private *dev_priv)
+ dev_priv->lvds_dither = 1;
  * intel_init_bios - initialize VBIOS settings & find VBT
  * @dev: DRM device
@@ -541,6 +550,7 @@ intel_init_bios(struct drm_device *dev)
  if (!vbt) {
  DRM_ERROR("VBT signature missing\n");
  pci_unmap_rom(pdev, bios);
+ get_no_vbt_default_settings(dev_priv);
  return -1;

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 14e21c3..94979a5 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -136,6 +136,15 @@ config DRM_I915_DIRECT_BACKLIGHT
   Direct backlight control gives finer granularity (0-256) than ACPI
   and does not require BIOS support.

+ bool "Set default BIOS settings when VBT is not found"
+ depends on DRM_I915
+ help
+  Choose this option if you want the i915 driver to set the device
+  settings to a set of defaults in the event that VBT is not found.
+  This will happen on systems with firmware that does not initialize
+  video.

 config DRM_MGA
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