[PATCH 3.16 054/114] drm/i915: Fix system resume if PCI device remained enabled

[Ben Hutchings]

3.16.36-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Imre Deak <imre.deak@xxxxxxxxx>

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)

CC: Ville SyrjÃlà <ville.syrjala@xxxxxxxxxxxxxxx>
CC: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
Reviewed-by: Ville SyrjÃlà <ville.syrjala@xxxxxxxxxxxxxxx>
Link: http://patchwork.freedesktop.org/patch/msgid/1460979954-14503-1-git-send-email-imre.deak@xxxxxxxxx
(cherry picked from commit 44410cd0bfb26bde9288da34c190cc9267d42a20)
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
[bwh: Backported to 3.16:
 - Return error code directly
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -686,6 +686,8 @@ static int i915_drm_thaw(struct drm_devi
 
 static int i915_resume_early(struct drm_device *dev)
 {
+	int ret;
+
 	if (dev->switch_power_state == DRM_SWITCH_POWER_OFF)
 		return 0;
 
@@ -698,6 +700,36 @@ static int i915_resume_early(struct drm_
 	 * 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);
+		return ret;
+	}
+
+	/*
+	 * 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))
 		return -EIO;