[Intel-gfx] [PATCH v2 1/3] drm/i915/guc: Temporarily bump the GuC load timeout

[John.C.Harrison at Intel.com]

From: John Harrison <John.C.Harrison at Intel.com>

There is a known (but exceedingly unlikely) race condition where the
asynchronous frequency management code could reduce the GT clock while
a GuC reload is in progress (during a full GT reset). A fix is in
progress but there are complex locking issues to be resolved. In the
meantime bump the timeout to 200ms. Even at slowest clock, this
should be sufficient. And in the working case, a larger timeout makes
no difference.

Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
Reviewed-by: Matthew Brost <matthew.brost at intel.com>
---
 drivers/gpu/drm/i915/gt/uc/intel_guc_fw.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_fw.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_fw.c
index 31420ce1ce6b..d09c205b2beb 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_fw.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_fw.c
@@ -105,12 +105,21 @@ static int guc_wait_ucode(struct intel_uncore *uncore)
 	/*
 	 * Wait for the GuC to start up.
 	 * NB: Docs recommend not using the interrupt for completion.
-	 * Measurements indicate this should take no more than 20ms, so a
+	 * Measurements indicate this should take no more than 20ms
+	 * (assuming the GT clock is at maximum frequency). So, a
 	 * timeout here indicates that the GuC has failed and is unusable.
 	 * (Higher levels of the driver may decide to reset the GuC and
 	 * attempt the ucode load again if this happens.)
+	 *
+	 * FIXME: There is a known (but exceedingly unlikely) race condition
+	 * where the asynchronous frequency management code could reduce
+	 * the GT clock while a GuC reload is in progress (during a full
+	 * GT reset). A fix is in progress but there are complex locking
+	 * issues to be resolved. In the meantime bump the timeout to
+	 * 200ms. Even at slowest clock, this should be sufficient. And
+	 * in the working case, a larger timeout makes no difference.
 	 */
-	ret = wait_for(guc_ready(uncore, &status), 100);
+	ret = wait_for(guc_ready(uncore, &status), 200);
 	if (ret) {
 		struct drm_device *drm = &uncore->i915->drm;
 
-- 
2.25.1