soc: qcom: rpmh-rsc: Remove the pm_lock

It has been postulated that the pm_lock is bad for performance because
a CPU currently running rpmh_flush() could block other CPUs from
coming out of idle.  Similarly CPUs coming out of / going into idle
all need to contend with each other for the spinlock just to update
the variable tracking who's in PM.

Let's optimize this a bit.  Specifically:

- Use a count rather than a bitmask.  This is faster to access and
  also means we can use the atomic_inc_return() function to really
  detect who the last one to enter PM was.
- Accept that it's OK if we race and are doing the flush (because we
  think we're last) while another CPU is coming out of idle.  As long
  as we block that CPU if/when it tries to do an active-only transfer
  we're OK.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20200504104917.v6.5.I295cb72bc5334a2af80313cbe97cb5c9dcb1442c@changeid
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

1 files changed, 16 insertions, 9 deletions

diff --git a/drivers/soc/qcom/rpmh.c b/drivers/soc/qcom/rpmh.c
index d1626a1328d7..f2b5b46ccd1f 100644
--- a/drivers/soc/qcom/rpmh.c
+++ b/drivers/soc/qcom/rpmh.c
@@ -435,9 +435,6 @@ static int send_single(struct rpmh_ctrlr *ctrlr, enum rpmh_state state,
  *
  * @ctrlr: Controller making request to flush cached data
  *
- * This function is called from sleep code on the last CPU
- * (thus no spinlock needed).
- *
  * Return:
  * * 0          - Success
  * * Error code - Otherwise
@@ -445,13 +442,21 @@ static int send_single(struct rpmh_ctrlr *ctrlr, enum rpmh_state state,
 int rpmh_flush(struct rpmh_ctrlr *ctrlr)
 {
 	struct cache_req *p;
-	int ret;
+	int ret = 0;
 
 	lockdep_assert_irqs_disabled();
 
+	/*
+	 * Currently rpmh_flush() is only called when we think we're running
+	 * on the last processor.  If the lock is busy it means another
+	 * processor is up and it's better to abort than spin.
+	 */
+	if (!spin_trylock(&ctrlr->cache_lock))
+		return -EBUSY;
+
 	if (!ctrlr->dirty) {
 		pr_debug("Skipping flush, TCS has latest data.\n");
-		return 0;
+		goto exit;
 	}
 
 	/* Invalidate the TCSes first to avoid stale data */
@@ -460,7 +465,7 @@ int rpmh_flush(struct rpmh_ctrlr *ctrlr)
 	/* First flush the cached batch requests */
 	ret = flush_batch(ctrlr);
 	if (ret)
-		return ret;
+		goto exit;
 
 	list_for_each_entry(p, &ctrlr->cache, list) {
 		if (!is_req_valid(p)) {
@@ -471,16 +476,18 @@ int rpmh_flush(struct rpmh_ctrlr *ctrlr)
 		ret = send_single(ctrlr, RPMH_SLEEP_STATE, p->addr,
 				  p->sleep_val);
 		if (ret)
-			return ret;
+			goto exit;
 		ret = send_single(ctrlr, RPMH_WAKE_ONLY_STATE, p->addr,
 				  p->wake_val);
 		if (ret)
-			return ret;
+			goto exit;
 	}
 
 	ctrlr->dirty = false;
 
-	return 0;
+exit:
+	spin_unlock(&ctrlr->cache_lock);
+	return ret;
 }
 
 /**