clk: si5351: msynth: Switch to determine_rate

The SI5351 msynth 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>
Link: https://lore.kernel.org/r/20221018-clk-range-checks-fixes-v4-55-971d5077e7d2@cerno.tech
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

Author: mripard

drivers/clk/clk-si5351.c

@@ -642,11 +642,12 @@ static unsigned long si5351_msynth_recalc_rate(struct clk_hw *hw,
 	return (unsigned long)rate;
 }
 
-static long si5351_msynth_round_rate(struct clk_hw *hw, unsigned long rate,
-				     unsigned long *parent_rate)
+static int si5351_msynth_determine_rate(struct clk_hw *hw,
+					struct clk_rate_request *req)
 {
 	struct si5351_hw_data *hwdata =
 		container_of(hw, struct si5351_hw_data, hw);
+	unsigned long rate = req->rate;
 	unsigned long long lltmp;
 	unsigned long a, b, c;
 	int divby4;
@@ -681,10 +682,10 @@ static long si5351_msynth_round_rate(struct clk_hw *hw, unsigned long rate,
 		b = 0;
 		c = 1;
 
-		*parent_rate = a * rate;
+		req->best_parent_rate = a * rate;
 	} else if (hwdata->num >= 6) {
 		/* determine the closest integer divider */
-		a = DIV_ROUND_CLOSEST(*parent_rate, rate);
+		a = DIV_ROUND_CLOSEST(req->best_parent_rate, rate);
 		if (a < SI5351_MULTISYNTH_A_MIN)
 			a = SI5351_MULTISYNTH_A_MIN;
 		if (a > SI5351_MULTISYNTH67_A_MAX)
@@ -702,15 +703,15 @@ static long si5351_msynth_round_rate(struct clk_hw *hw, unsigned long rate,
 		}
 
 		/* determine integer part of divider equation */
-		a = *parent_rate / rate;
+		a = req->best_parent_rate / rate;
 		if (a < SI5351_MULTISYNTH_A_MIN)
 			a = SI5351_MULTISYNTH_A_MIN;
 		if (a > SI5351_MULTISYNTH_A_MAX)
 			a = SI5351_MULTISYNTH_A_MAX;
 
 		/* find best approximation for b/c = fVCO mod fOUT */
 		denom = 1000 * 1000;
-		lltmp = (*parent_rate) % rate;
+		lltmp = req->best_parent_rate % rate;
 		lltmp *= denom;
 		do_div(lltmp, rate);
 		rfrac = (unsigned long)lltmp;
@@ -724,7 +725,7 @@ static long si5351_msynth_round_rate(struct clk_hw *hw, unsigned long rate,
 	}
 
 	/* recalculate rate by fOUT = fIN / (a + b/c) */
-	lltmp  = *parent_rate;
+	lltmp  = req->best_parent_rate;
 	lltmp *= c;
 	do_div(lltmp, a * c + b);
 	rate  = (unsigned long)lltmp;
@@ -749,9 +750,11 @@ static long si5351_msynth_round_rate(struct clk_hw *hw, unsigned long rate,
 	dev_dbg(&hwdata->drvdata->client->dev,
 		"%s - %s: a = %lu, b = %lu, c = %lu, divby4 = %d, parent_rate = %lu, rate = %lu\n",
 		__func__, clk_hw_get_name(hw), a, b, c, divby4,
-		*parent_rate, rate);
+		req->best_parent_rate, rate);
 
-	return rate;
+	req->rate = rate;
+
+	return 0;
 }
 
 static int si5351_msynth_set_rate(struct clk_hw *hw, unsigned long rate,
@@ -791,7 +794,7 @@ static const struct clk_ops si5351_msynth_ops = {
 	.set_parent = si5351_msynth_set_parent,
 	.get_parent = si5351_msynth_get_parent,
 	.recalc_rate = si5351_msynth_recalc_rate,
-	.round_rate = si5351_msynth_round_rate,
+	.determine_rate = si5351_msynth_determine_rate,
 	.set_rate = si5351_msynth_set_rate,
 };