[alsa-devel] [PATCH 5/6] clk: at91: clk-generated: make gclk determine audio_pll rate

[Quentin Schulz]

This allows gclk to determine audio_pll rate and set the parent rate
accordingly.

However, there are multiple children clocks that could technically
change the rate of audio_pll. Since the clock rate is usually critical
for IPs, it isn't a good idea to have multiple clocks changing audio_pll
clock rate. There isn't any rate locking system for the moment, thus
we enforce that classd_gclk be the only one allowed to change audio_pll
rate. To remain consistent, we deny other clocks to be children of
audio_pll so classd_gclk altering audio_pll rate does not impact any
other device.

This needs to be re-worked once we have a rate locking system so two
clocks could be children of the same clock and be sure the clock rate
isn't changed by one or the other.

Signed-off-by: Quentin Schulz <quentin.schulz at free-electrons.com>
---
 drivers/clk/at91/clk-generated.c | 41 ++++++++++++++++++++++++++++++++++------
 1 file changed, 35 insertions(+), 6 deletions(-)

diff --git a/drivers/clk/at91/clk-generated.c b/drivers/clk/at91/clk-generated.c
index 6530a2e7e84d..e66ee735a569 100644
--- a/drivers/clk/at91/clk-generated.c
+++ b/drivers/clk/at91/clk-generated.c
@@ -26,6 +26,9 @@
 #define GENERATED_SOURCE_MAX	6
 #define GENERATED_MAX_DIV	255
 
+#define GCK_ID_CLASSD		59
+#define GCK_INDEX_DT_AUDIO_PLL	5
+
 struct clk_generated {
 	struct clk_hw hw;
 	struct regmap *regmap;
@@ -126,15 +129,14 @@ static int clk_generated_determine_rate(struct clk_hw *hw,
 {
 	struct clk_generated *gck = to_clk_generated(hw);
 	struct clk_hw *parent = NULL;
+	struct clk_rate_request req_parent = *req;
 	long best_rate = -EINVAL;
-	unsigned long min_rate;
+	unsigned long min_rate, parent_rate;
 	int best_diff = -1;
 	int i;
+	u32 div;
 
-	for (i = 0; i < clk_hw_get_num_parents(hw); i++) {
-		u32 div;
-		unsigned long parent_rate;
-
+	for (i = 0; i < clk_hw_get_num_parents(hw) - 1; i++) {
 		parent = clk_hw_get_parent_by_index(hw, i);
 		if (!parent)
 			continue;
@@ -150,11 +152,37 @@ static int clk_generated_determine_rate(struct clk_hw *hw,
 		clk_generated_best_diff(req, parent, parent_rate, div,
 					&best_diff, &best_rate);
 
+		if (!best_diff)
+			break;
+	}
+
+	/*
+	 * The audio_pll rate can be modified unlike the five others clocks that
+	 * should never be altered.
+	 * The audio_pll can technically be used by multiple consumers. However,
+	 * they all are likely to want to modify its rate while the rate is
+	 * critical for each one. Since we do not have a rate locking for the
+	 * moment, let classd_gclk be the only consumer of the audio_pll clock.
+	 */
+
+	if (gck->id != GCK_ID_CLASSD)
+		goto end;
+
+	parent = clk_hw_get_parent_by_index(hw, GCK_INDEX_DT_AUDIO_PLL);
+	if (!parent)
+		goto end;
+
+	for (div = 1; div < GENERATED_MAX_DIV + 2; div++) {
+		req_parent.rate = req->rate * div;
+		__clk_determine_rate(parent, &req_parent);
+		clk_generated_best_diff(req, parent, req_parent.rate, div,
+					&best_diff, &best_rate);
 
 		if (!best_diff)
 			break;
 	}
 
+end:
 	pr_debug("GCLK: %s, best_rate = %ld, parent clk: %s @ %ld\n",
 		 __func__, best_rate,
 		 __clk_get_name((req->best_parent_hw)->clk),
@@ -264,7 +292,8 @@ at91_clk_register_generated(struct regmap *regmap, spinlock_t *lock,
 	init.ops = &generated_ops;
 	init.parent_names = parent_names;
 	init.num_parents = num_parents;
-	init.flags = CLK_SET_RATE_GATE | CLK_SET_PARENT_GATE;
+	init.flags = CLK_SET_RATE_GATE | CLK_SET_PARENT_GATE |
+		CLK_SET_RATE_PARENT;
 
 	gck->id = id;
 	gck->hw.init = &init;
-- 
2.11.0