[Intel-gfx] [PATCH] drm/i915: Do graphics device reset under forcewake

[Mika Kuoppala]

We have a timed release of a forcewake when using
I915_READ/WRITE macros. wait_for() macro will go to quite
long sleep if the first read doesn't satisfy the condition for
successful exit. With these two interacting, it is possible that
we lose the forcewake during the wait_for() and the subsequent read
will reaquire forcewake.

Further experiments with skl shows that when we lose forcewake,
we lose the reset request we submitted. So reset request register
is not power context saved.

Grab forcewakes for all engines before starting the reset/request
dance so that all requests stay valid for the duration of reset
requisition across all the engines.

v2: Add comment on power well sleeps. Wrap the reset handling
    under forcewake instead of just reset requests (Chris)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92774
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Tested-by: Tomi Sarvela <tomix.p.sarvela at intel.com> (v1, v2)
Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
---
 drivers/gpu/drm/i915/intel_uncore.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index f0f97b2..5bb269c 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -1530,13 +1530,22 @@ static int (*intel_get_gpu_reset(struct drm_device *dev))(struct drm_device *)
 
 int intel_gpu_reset(struct drm_device *dev)
 {
+	struct drm_i915_private *dev_priv = to_i915(dev);
 	int (*reset)(struct drm_device *);
+	int ret;
 
 	reset = intel_get_gpu_reset(dev);
 	if (reset == NULL)
 		return -ENODEV;
 
-	return reset(dev);
+	/* If the power well sleeps during the reset, the reset
+	 * request may be dropped and never completes (causing -EIO).
+	 */
+	intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);
+	ret = reset(dev);
+	intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);
+
+	return ret;
 }
 
 bool intel_has_gpu_reset(struct drm_device *dev)
-- 
2.5.0