[PATCH 3.12 075/144] drm/i915: change CRTC assertion on LCPLL disable

From: Greg Kroah-Hartman
Date: Mon Jan 06 2014 - 18:59:28 EST

3.12-stable review patch. If anyone has any objections, please let me know.


From: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx>

commit 96b4026878d9dac71bd4c3d6e05c7fbb16a3e0aa upstream.

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@xxxxxxxxx>
(cherry picked from commit 798183c54799fbe1e5a5bfabb3a8c0505ffd2149
from -next due to Dave's report.)
Reported-by: Dave Jones <davej@xxxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/gpu/drm/i915/intel_display.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6009,7 +6009,7 @@ static void assert_can_disable_lcpll(str
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",

WARN(I915_READ(HSW_PWR_WELL_DRIVER), "Power well on\n");

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