[PATCH v2 50/65] clk: si5341: Switch to determine_rate

Maxime Ripard
2022-11-04T13:34:51Z

The SI5341 output clocks implements a mux with a set_parent hook, but
doesn't provide a determine_rate implementation.

This is a bit odd, since set_parent() is there to, as its name implies,
change the parent of a clock. However, the most likely candidate to
trigger that parent change is a call to clk_set_rate(), with
determine_rate() figuring out which parent is the best suited for a
given rate.

The other trigger would be a call to clk_set_parent(), but it's far less
used, and it doesn't look like there's any obvious user for that clock.

So, the set_parent hook is effectively unused, possibly because of an
oversight. However, it could also be an explicit decision by the
original author to avoid any reparenting but through an explicit call to
clk_set_parent().

The driver does implement round_rate() though, which means that we can
change the rate of the clock, but we will never get to change the
parent.

However, It's hard to tell whether it's been done on purpose or not.

Since we'll start mandating a determine_rate() implementation, let's
convert the round_rate() implementation to a determine_rate(), which
will also make the current behavior explicit. And if it was an
oversight, the clock behaviour can be adjusted later on.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
drivers/clk/clk-si5341.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/clk/clk-si5341.c b/drivers/clk/clk-si5341.c
index 259861aa2e2f..14792d5ffb4f 100644
--- a/drivers/clk/clk-si5341.c
+++ b/drivers/clk/clk-si5341.c
@@ -828,19 +828,20 @@ static unsigned long si5341_output_clk_recalc_rate(struct clk_hw *hw,
return parent_rate / r_divider;
}

-static long si5341_output_clk_round_rate(struct clk_hw *hw, unsigned long rate,
- unsigned long *parent_rate)
+static int si5341_output_clk_determine_rate(struct clk_hw *hw,
+ struct clk_rate_request *req)
{
+ unsigned long rate = req->rate;
unsigned long r;

if (!rate)
return 0;

- r = *parent_rate >> 1;
+ r = req->best_parent_rate >> 1;

/* If rate is an even divisor, no changes to parent required */
if (r && !(r % rate))
- return (long)rate;
+ return 0;

if (clk_hw_get_flags(hw) & CLK_SET_RATE_PARENT) {
if (rate > 200000000) {
@@ -850,14 +851,15 @@ static long si5341_output_clk_round_rate(struct clk_hw *hw, unsigned long rate,
/* Take a parent frequency near 400 MHz */
r = (400000000u / rate) & ~1;
}
- *parent_rate = r * rate;
+ req->best_parent_rate = r * rate;
} else {
/* We cannot change our parent's rate, report what we can do */
r /= rate;
- rate = *parent_rate / (r << 1);
+ rate = req->best_parent_rate / (r << 1);
}

- return rate;
+ req->rate = rate;
+ return 0;
}

static int si5341_output_clk_set_rate(struct clk_hw *hw, unsigned long rate,
@@ -930,7 +932,7 @@ static const struct clk_ops si5341_output_clk_ops = {
.prepare = si5341_output_clk_prepare,
.unprepare = si5341_output_clk_unprepare,
.recalc_rate = si5341_output_clk_recalc_rate,
- .round_rate = si5341_output_clk_round_rate,
+ .determine_rate = si5341_output_clk_determine_rate,
.set_rate = si5341_output_clk_set_rate,
.set_parent = si5341_output_set_parent,
.get_parent = si5341_output_get_parent,

--
b4 0.11.0-dev-99e3a