[Intel-gfx] [PATCH 4/4] drm/i915: Acquire PUNIT->PMIC bus for intel_uncore_forcewake_reset()

[Hans de Goede]

intel_uncore_forcewake_reset() does forcewake puts and gets as such
we need to make sure that no-one tries to access the PUNIT->PMIC bus
(on systems where this bus is shared) while it runs, otherwise bad
things happen.

Normally this is taken care of by the i915_pmic_bus_access_notifier()
which does an intel_uncore_forcewake_get(FORCEWAKE_ALL) when some other
driver tries to access the PMIC bus, so that later forcewake gets are
no-ops (for the duration of the bus access).

But intel_uncore_forcewake_reset gets called in 3 cases:
1) Before registering the pmic_bus_access_notifier
2) After unregistering the pmic_bus_access_notifier
3) To reset forcewake state on a GPU reset

In all 3 cases the i915_pmic_bus_access_notifier() protection is
insufficient. This commit fixes the pmic bus access race this causes
by making intel_uncore_forcewake_reset() call iosf_mbi_punit_acquire()
(and iosf_mbi_punit_release() when done).

Note that iosf_mbi_punit_acquire() locks a mutex and thus
intel_uncore_forcewake_reset() may sleep after this commit. I've checked
all callers and they all already take other mutexes, so this is not a
problem.

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/i915/intel_uncore.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index 882cf7187a57..0fb829cc1cbd 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -252,6 +252,9 @@ static void intel_uncore_forcewake_reset(struct drm_i915_private *dev_priv,
 	int retry_count = 100;
 	enum forcewake_domains fw, active_domains;
 
+	/* Acquire the PUNIT->PMIC bus before modifying forcewake settings */
+	iosf_mbi_punit_acquire();
+
 	/* Hold uncore.lock across reset to prevent any register access
 	 * with forcewake not set correctly. Wait until all pending
 	 * timers are run before holding.
@@ -308,6 +311,7 @@ static void intel_uncore_forcewake_reset(struct drm_i915_private *dev_priv,
 		assert_forcewakes_inactive(dev_priv);
 
 	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
+	iosf_mbi_punit_release();
 }
 
 static u64 gen9_edram_size(struct drm_i915_private *dev_priv)
-- 
2.12.2