drm/i915: change CRTC assertion on LCPLL disable

Currently, PC8 is enabled at modeset_global_resources, which is called
after intel_modeset_update_state. Due to this, there's a small race
condition on the case where we start enabling PC8, then do a modeset
while PC8 is still being enabled. The racing condition triggers a WARN
because intel_modeset_update_state will mark the CRTC as enabled, then
the thread that's still enabling PC8 might look at the data structure
and think that PC8 is being enabled while a pipe is enabled. Despite
the WARN, this is not really a bug since we'll wait for the
PC8-enabling thread to finish when we call modeset_global_resources.

The spec says the CRTC cannot be enabled when we disable LCPLL, so we
had a check for crtc->base.enabled. If we change to crtc->active we
will still prevent disabling LCPLL while the CRTC is enabled, and we
will also prevent the WARN above.

This is a replacement for the previous patch named
    "drm/i915: get/put PC8 when we get/put a CRTC"

Testcase: igt/pm_pc8/modeset-lpsp-stress-no-wait
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
(cherry picked from commit 798183c547
from -next due to Dave's report.)
Reported-by: Dave Jones <davej@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -6303,7 +6303,7 @@ static void assert_can_disable_lcpll(struct drm_i915_private *dev_priv)
 	uint32_t val;
 
 	list_for_each_entry(crtc, &dev->mode_config.crtc_list, base.head)
-		WARN(crtc->base.enabled, "CRTC for pipe %c enabled\n",
+		WARN(crtc->active, "CRTC for pipe %c enabled\n",
 		     pipe_name(crtc->pipe));
 
 	WARN(I915_READ(HSW_PWR_WELL_DRIVER), "Power well on\n");