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clk: Remove global clk traversal on fetch parent index

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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 470b5e2f97 ("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 da0f0b2c3a ("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>
This commit is contained in:
Derek Basehore 2018-12-20 16:31:00 -08:00 committed by Stephen Boyd
parent 401fbb34f5
commit ede7785847
1 changed files with 12 additions and 2 deletions
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14
drivers/clk/clk.c
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@ -1513,10 +1513,20 @@ 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;
}