drm/i915: do not disable backlight on vgaswitcheroo switch off

On muxed systems, the other vgaswitcheroo client may depend on i915 to
handle the backlight. We began switching off the backlight since

commit 3a9e2a5395a2ffcd6ddb1c7cd5ab98222197fd26
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Thu Jul 26 19:21:47 2012 +0200

    drm/i915: disable all crtcs at suspend time

breaking backlight on discreet graphics in (some) muxed systems.

Keep the backlight on when the state is changed through vgaswitcheroo.

Note: The alternative would be to add a quirk table to achieve the same
based on system identifiers, but AFAICS it would asymptotically approach
effectively the same as this patch as more IDs are added, but with the
maintenance burden of the quirk table.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=55311
Tested-by: Fede <fedevx@yahoo.com>
Tested-by: Aximab <laurent.debian@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=59785
Tested-by: sfievet <sebastien.fievet@free.fr>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 5063eadac3ef5fc1a2966ccb081ae4bc2aaf8ad1..5950888ae1d00bd7cf70ebb18d5595ee0ee8446e 100644 (file)
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -518,6 +518,17 @@ void intel_panel_disable_backlight(struct drm_device *dev)
        struct drm_i915_private *dev_priv = dev->dev_private;
        unsigned long flags;
 
+       /*
+        * Do not disable backlight on the vgaswitcheroo path. When switching
+        * away from i915, the other client may depend on i915 to handle the
+        * backlight. This will leave the backlight on unnecessarily when
+        * another client is not activated.
+        */
+       if (dev->switch_power_state == DRM_SWITCH_POWER_CHANGING) {
+               DRM_DEBUG_DRIVER("Skipping backlight disable on vga switch\n");
+               return;
+       }
+
        spin_lock_irqsave(&dev_priv->backlight.lock, flags);
 
        dev_priv->backlight.enabled = false;