[Intel-gfx] [RFC PATCH 02/10] drm/i915/guc: Add CT size delay helper

[Jonathan Cavitt]

Add a helper function to the GuC CT buffer that reports the expected
time to process all outstanding requests.  As of now, there is no
functionality to check number of requests in the buffer, so the helper
function just reports 2 seconds, or 1ms per request up to the maximum
number of requests the CT buffer can store.

Suggested-by: John Harrison <john.c.harrison at intel.com>
Signed-off-by: Jonathan Cavitt <jonathan.cavitt at intel.com>
---
 drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
index 58e42901ff498..36afc1ce9fabd 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
@@ -120,6 +120,19 @@ static inline bool intel_guc_ct_enabled(struct intel_guc_ct *ct)
 	return ct->enabled;
 }
 
+/*
+ * GuC has a timeout of 1ms for a TLB invalidation response from GAM.  On a
+ * timeout GuC drops the request and has no mechanism to notify the host about
+ * the timeout.  There is also no mechanism for determining the number of
+ * outstanding requests in the CT buffer.  Ergo, keep a larger timeout that accounts
+ * for this individual timeout and the max number of outstanding requests that
+ * can be queued in CT buffer.
+ */
+static inline long intel_guc_ct_expected_delay(struct intel_guc_ct *ct)
+{
+	return HZ * 2;
+}
+
 #define INTEL_GUC_CT_SEND_NB		BIT(31)
 #define INTEL_GUC_CT_SEND_G2H_DW_SHIFT	0
 #define INTEL_GUC_CT_SEND_G2H_DW_MASK	(0xff << INTEL_GUC_CT_SEND_G2H_DW_SHIFT)
-- 
2.25.1