linux-kernel - [PATCH] clk: Remove global clk traversal on fetch parent index

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Date:   Thu, 20 Dec 2018 16:31:00 -0800
From:   Derek Basehore <dbasehore@...omium.org>
To:     mturquette@...libre.com
Cc:     sboyd@...nel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Derek Basehore <dbasehore@...omium.org>
Subject: [PATCH] clk: Remove global clk traversal on fetch parent index

It's not required to traverse the entire clk tree when the parents
array contains a NULL value. You already have the parent clk_core
pointer, so you can just compare the parent->name and parent_names[i]
pointers.

In cases where clk names are never registered, this can be
a substantial power improvement since a mux having an unregistered
parent name will traverse the clk tree on every set_rate. This can
happen hundreds of times a second on CPU clks.

Change-Id: I85499d2e576249568ff508e424ca8d5009e6e2b1
Signed-off-by: Derek Basehore <dbasehore@...omium.org>
---
 drivers/clk/clk.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index af011974d4ec..57a95c713286 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1516,9 +1516,18 @@ static int clk_fetch_parent_index(struct clk_core *core,
 	if (!parent)
 		return -EINVAL;
 
-	for (i = 0; i < core->num_parents; i++)
-		if (clk_core_get_parent_by_index(core, i) == parent)
+	for (i = 0; i < core->num_parents; i++) {
+		if (core->parents[i] == parent)
+			return i;
+
+		if (core->parents[i])
+			continue;
+
+		if (!strcmp(parent->name, core->parent_names[i])) {
+			core->parents[i] = parent;
 			return i;
+		}
+	}
 
 	return -EINVAL;
 }
-- 
2.20.1.415.g653613c723-goog