Patch "drm/i915: Fix system resume if PCI device remained enabled" has been added to the 4.5-stable tree

This is a note to let you know that I've just added the patch titled

drm/i915: Fix system resume if PCI device remained enabled

to the 4.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-i915-fix-system-resume-if-pci-device-remained-enabled.patch
and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Imre Deak <[email protected]>
Date: Mon, 18 Apr 2016 14:45:54 +0300
Subject: drm/i915: Fix system resume if PCI device remained enabled
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From: Imre Deak <[email protected]>

commit dab9a2663f4e688106c041f7cd2797a721382f0a upstream.

During system resume we depended on pci_enable_device() also putting the device into PCI D0 state. This won't work if the PCI device was already enabled but still in D3 state. This is because pci_enable_device() is refcounted and will not change the HW state if called with a non-zero refcount. Leaving the device in D3 will make all subsequent device accesses fail.

This didn't cause a problem most of the time, since we resumed with an enable refcount of 0. But it fails at least after module reload because after that we also happen to leak a PCI device enable reference: During probing we call drm_get_pci_dev() which will enable the PCI device, but during device removal drm_put_dev() won't disable it. This is a bug of its own in DRM core, but without much harm as it only leaves the PCI device enabled. Fixing it is also a bit more involved, due to DRM mid-layering and because it affects non-i915 drivers too. The fix in this patch is valid regardless of the problem in DRM core.

v2:
- Add a code comment about the relation of this fix to the freeze/thaw vs. the suspend/resume phases. (Ville)
- Add a code comment about the inconsistent ordering of set power state and device enable calls. (Chris)

---
 drivers/gpu/drm/i915/i915_drv.c |   32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

@@ -797,7 +797,7 @@ static int i915_drm_resume(struct drm_de
 static int i915_drm_resume_early(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	int ret = 0;
+	int ret;
 
 	/*
 	 * We have a resume ordering issue with the snd-hda driver also

@@ -808,6 +808,36 @@ static int i915_drm_resume_early(struct
 	 * FIXME: This should be solved with a special hdmi sink device or
 	 * similar so that power domains can be employed.
 	 */
+
+	/*
+	 * Note that we need to set the power state explicitly, since we
+	 * powered off the device during freeze and the PCI core won't power
+	 * it back up for us during thaw. Powering off the device during
+	 * freeze is not a hard requirement though, and during the
+	 * suspend/resume phases the PCI core makes sure we get here with the
+	 * device powered on. So in case we change our freeze logic and keep
+	 * the device powered we can also remove the following set power state
+	 * call.
+	 */
+	ret = pci_set_power_state(dev->pdev, PCI_D0);
+	if (ret) {
+		DRM_ERROR("failed to set PCI D0 power state (%d)\n", ret);
+		goto out;
+	}
+
+	/*
+	 * Note that pci_enable_device() first enables any parent bridge
+	 * device and only then sets the power state for this device. The
+	 * bridge enabling is a nop though, since bridge devices are resumed
+	 * first. The order of enabling power and enabling the device is
+	 * imposed by the PCI core as described above, so here we preserve the
+	 * same order for the freeze/thaw phases.
+	 *
+	 * TODO: eventually we should remove pci_disable_device() /
+	 * pci_enable_enable_device() from suspend/resume. Due to how they
+	 * depend on the device enable refcount we can't anyway depend on them
+	 * disabling/enabling the device.
+	 */
 	if (pci_enable_device(dev->pdev)) {
 		ret = -EIO;
 		goto out;

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/drm-i915-ddi-fix-edp-vdd-handling-during-booting-and-suspend-resume.patch queue-4.5/drm-i915-fix-system-resume-if-pci-device-remained-enabled.patch