On 05/20/2013 06:28 AM, James Hogan wrote:
Implement clk-mux remuxing if the CLK_SET_RATE_NO_REPARENT flag isn't
set. This implements determine_rate for clk-mux to propagate to each
parent and to choose the best one (like clk-divider this chooses the
parent which provides the fastest rate <= the requested rate).
The determine_rate op is implemented as a core helper function so that
it can be easily used by more complex clocks which incorporate muxes.
Signed-off-by: James Hogan <james.ho...@imgtec.com>
Cc: Mike Turquette <mturque...@linaro.org>
Cc: linux-arm-ker...@lists.infradead.org
---
Changes in v4:
* never pass NULL to determine_rate's best_parent_clk parameter.
Changes in v3:
* rename/invert CLK_SET_RATE_REMUX to CLK_SET_RATE_NO_REPARENT and move
to patch 3.
drivers/clk/clk-mux.c | 1 +
drivers/clk/clk.c | 49 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/clk-provider.h | 3 +++
3 files changed, 53 insertions(+)
diff --git a/drivers/clk/clk-mux.c b/drivers/clk/clk-mux.c
index 25b1734..cecfa01 100644
--- a/drivers/clk/clk-mux.c
+++ b/drivers/clk/clk-mux.c
@@ -100,6 +100,7 @@ static int clk_mux_set_parent(struct clk_hw *hw, u8 index)
const struct clk_ops clk_mux_ops = {
.get_parent = clk_mux_get_parent,
.set_parent = clk_mux_set_parent,
+ .determine_rate = __clk_mux_determine_rate,
};
EXPORT_SYMBOL_GPL(clk_mux_ops);
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 3ce4810..85b661d 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -692,6 +692,55 @@ struct clk *__clk_lookup(const char *name)
return NULL;
}
+/*
+ * Helper for finding best parent to provide a given frequency. This can be
used
+ * directly as a determine_rate callback (e.g. for a mux), or from a more
+ * complex clock that may combine a mux with other operations.
+ */
+long __clk_mux_determine_rate(struct clk_hw *hw, unsigned long rate,
+ unsigned long *best_parent_rate,
+ struct clk **best_parent_p)
+{
+ struct clk *clk = hw->clk, *parent, *best_parent = NULL;
+ int i, num_parents;
+ unsigned long parent_rate, best = 0;
+
+ /* if NO_REPARENT flag set, pass through to current parent */
+ if (clk->flags & CLK_SET_RATE_NO_REPARENT) {
+ parent = clk->parent;
+ if (clk->flags & CLK_SET_RATE_PARENT)
+ best = __clk_round_rate(parent, rate);
+ else if (parent)
+ best = __clk_get_rate(parent);
+ else
+ best = __clk_get_rate(clk);
+ goto out;
+ }
+
+ /* find the parent that can provide the fastest rate <= rate */
+ num_parents = clk->num_parents;
+ for (i = 0; i < num_parents; i++) {
While writing a similar code for our internal tree, I quickly came to
the realization that, "all parents are equal, but some are more equal
than others". The simplest example is a clock tree like this:
Source -> Divider -> Mux
Source -> Mux
A rate of Y can be achieved for Mux by either running Source at Y and
picking that input or running Source at Y * 2 and Divider set to div-2
and picking the Divider input.
The solution seems to be a priority list of parents. I'm sure there
would be other reason (jitter, clock quality, etc) for a mux to pick one
parent vs. another when both of them can provide the required rate.
I think this loop should loop over parents based on their priority
order. So, parents should become a struct of { clk, index } and have the
parents listed in the order of priority. Well, at least in that long run
that would be better to avoid messing up parent/index values. But for
now, you could just have a priority array of index or parents.
It might not fit 100% of the cases where two parents can provide the
same rate, but it should fit most use cases.
+ parent = clk_get_parent_by_index(clk, i);
+ if (!parent)
+ continue;
+ if (clk->flags & CLK_SET_RATE_PARENT)
+ parent_rate = __clk_round_rate(parent, rate);
+ else
+ parent_rate = __clk_get_rate(parent);
+ if (parent_rate <= rate && parent_rate > best) {
+ best_parent = parent;
+ best = parent_rate;
+ }
+ }
+
+out:
+ if (best_parent)
+ *best_parent_p = best_parent;
+ *best_parent_rate = best;
+
+ return best;
+}
+
Thanks,
Saravana
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