drm/i915/pxp: start the arb session on demand

Now that we can handle destruction and re-creation of the arb session,
we can postpone the start of the session to the first submission that
requires it, to avoid keeping it running with no user.

v10: increase timeout when waiting in intel_pxp_start as firmware
     session startup is slower right after boot.
v13: increase the same timeout by 50 milisec because previous timeout
     was not enough to cover two lower level 100 milisec timeouts
     in the session termination + creation steps.

Signed-off-by: Alan Previn <alan.previn.teres.alexis@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210924191452.1539378-12-alan.previn.teres.alexis@intel.com

1 files changed, 24 insertions, 13 deletions

diff --git a/drivers/gpu/drm/i915/pxp/intel_pxp.c b/drivers/gpu/drm/i915/pxp/intel_pxp.c
index ee507fd8ae19..7f241c0218c1 100644
--- a/drivers/gpu/drm/i915/pxp/intel_pxp.c
+++ b/drivers/gpu/drm/i915/pxp/intel_pxp.c
@@ -91,6 +91,7 @@ void intel_pxp_init(struct intel_pxp *pxp)
 	init_completion(&pxp->termination);
 	complete_all(&pxp->termination);
 
+	mutex_init(&pxp->arb_mutex);
 	INIT_WORK(&pxp->session_work, intel_pxp_session_work);
 
 	ret = create_vcs_context(pxp);
@@ -127,7 +128,7 @@ void intel_pxp_mark_termination_in_progress(struct intel_pxp *pxp)
 	reinit_completion(&pxp->termination);
 }
 
-static void intel_pxp_queue_termination(struct intel_pxp *pxp)
+static void pxp_queue_termination(struct intel_pxp *pxp)
 {
 	struct intel_gt *gt = pxp_to_gt(pxp);
 
@@ -146,31 +147,41 @@ static void intel_pxp_queue_termination(struct intel_pxp *pxp)
  * the arb session is restarted from the irq work when we receive the
  * termination completion interrupt
  */
-int intel_pxp_wait_for_arb_start(struct intel_pxp *pxp)
+int intel_pxp_start(struct intel_pxp *pxp)
 {
+	int ret = 0;
+
 	if (!intel_pxp_is_enabled(pxp))
-		return 0;
+		return -ENODEV;
+
+	mutex_lock(&pxp->arb_mutex);
+
+	if (pxp->arb_is_valid)
+		goto unlock;
+
+	pxp_queue_termination(pxp);
 
 	if (!wait_for_completion_timeout(&pxp->termination,
-					 msecs_to_jiffies(100)))
-		return -ETIMEDOUT;
+					msecs_to_jiffies(250))) {
+		ret = -ETIMEDOUT;
+		goto unlock;
+	}
+
+	/* make sure the compiler doesn't optimize the double access */
+	barrier();
 
 	if (!pxp->arb_is_valid)
-		return -EIO;
+		ret = -EIO;
 
-	return 0;
+unlock:
+	mutex_unlock(&pxp->arb_mutex);
+	return ret;
 }
 
 void intel_pxp_init_hw(struct intel_pxp *pxp)
 {
 	kcr_pxp_enable(pxp_to_gt(pxp));
 	intel_pxp_irq_enable(pxp);
-
-	/*
-	 * the session could've been attacked while we weren't loaded, so
-	 * handle it as if it was and re-create it.
-	 */
-	intel_pxp_queue_termination(pxp);
 }
 
 void intel_pxp_fini_hw(struct intel_pxp *pxp)