drm/i915: check the power well when redisabling VGA

If the power well is disabled VGA is guaranteed to be disabled.

This fixes unclaimed register messages that happen on suspend/resume.

v2: Check the actual hw power well state instead of our own tracking
to make sure VGA is _really_ off (in case the BIOS/KVMr has just its
own request bit set). Requested by Ville.

Note: Ville suggested whether it wouldn't be better to just enable the
power well over a slightly longer time in our resume code, since we
already do that. I tend to agree, but there's also the modeset force
code in the lid notifier which _also_ eventually calls redisable_vga.
We shouldn't ever need this on somewhat modern hw (everything with
opregion essentially) but the code to bail out isn't there. Hence
stick with this simple approach here for now.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67517
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
[danvet: Summarize the discussion around the resume sequence and lid
notifier a bit.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index a87bb93a0f63b971d32b3bc8a1961baa6f2cb64c..f83316ec0b94134ab6866c65d758962cc5acff5c 100644 (file)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -10104,6 +10104,17 @@ void i915_redisable_vga(struct drm_device *dev)
        struct drm_i915_private *dev_priv = dev->dev_private;
        u32 vga_reg = i915_vgacntrl_reg(dev);
 
+       /* This function can be called both from intel_modeset_setup_hw_state or
+        * at a very early point in our resume sequence, where the power well
+        * structures are not yet restored. Since this function is at a very
+        * paranoid "someone might have enabled VGA while we were not looking"
+        * level, just check if the power well is enabled instead of trying to
+        * follow the "don't touch the power well if we don't need it" policy
+        * the rest of the driver uses. */
+       if (HAS_POWER_WELL(dev) &&
+           (I915_READ(HSW_PWR_WELL_DRIVER) & HSW_PWR_WELL_STATE) == 0)
+               return;
+
        if (I915_READ(vga_reg) != VGA_DISP_DISABLE) {
                DRM_DEBUG_KMS("Something enabled VGA plane, disabling it\n");
                i915_disable_vga(dev);