Commit ede77858 authored Dec 20, 2018 by Derek Basehore Committed by Stephen Boyd Jan 24, 2019

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. We already have the parent clk_core pointer, so
we can just compare the parent->name and parent_names[i] pointers.

This can be a substantial power improvement in cases where the parent
clk isn't known and that clk is never registered, because a mux having
an unregistered parent name may traverse the clk tree on every
clk_set_rate() call in clk_mux_determine_rate_flags(). This can happen
hundreds of times a second for CPU clks.

This patch is the combination of reverting commit 470b5e2f ("clk:
simplify clk_fetch_parent_index() function") and optimizing the
resulting code to never call __clk_lookup() because we already have the
clk_core pointer we're looking for. That optimization went unnoticed
even after commit da0f0b2c ("clk: Correct lookup logic in
clk_fetch_parent_index()") tried to optimize this path.

Signed-off-by: Derek Basehore <dbasehore@chromium.org>
[sboyd@kernel.org: More description in commit text]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

parent 401fbb34

drivers/clk/clk.c

+12 −2

Original line number	Diff line number	Diff line
		@@ -1513,9 +1513,19 @@ 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;

		/* Fallback to comparing globally unique names */
		if (!strcmp(parent->name, core->parent_names[i])) {
		core->parents[i] = parent;
		return i;
		}
		}

		return -EINVAL;
		}