[PATCH v3 1/5] clk: scmi: Allocate CLK operations dynamically

[Cristian Marussi <cristian.marussi@arm.com>]

SCMI Clocks descriptors expose an increasing number of properties, thing
which, in turn, leads to a varying set of supported CLK operations to be
associated with each clock.

Providing statically pre-defined CLK operations structs for all the
possible combinations of allowed clock features is becoming cumbersome and
error-prone.

Allocate the per-clock operations descriptors dynamically and populate it
with the strictly needed set of operations depending on the advertised
clock properties: one descriptor is created for each distinct combination
of clock operations, so minimizing the number of clk_ops structures to the
strictly minimum needed.

CC: Michael Turquette <mturquette@baylibre.com>
CC: Stephen Boyd <sboyd@kernel.org>
CC: linux-clk@vger.kernel.org
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
v2 --> v3
- moving scmi_clk_ops_db from being global to a per-instance/per-probe
  structure to avoid sharing devm_ allocated clk_ops between different driver
  instances.
- using bits.h
- fixed a few dox comments
- explicit unit in atomic_threshold_us
- added a runtime size-check before accessing scmi_clk_ops_db using feats_key
- reworked scmi_clk_ops_alloc call to reduce nesting
- transport_is_atomic instead of is_atomic to be clearer
---
 drivers/clk/clk-scmi.c | 186 ++++++++++++++++++++++++++++++-----------
 1 file changed, 136 insertions(+), 50 deletions(-)

diff --git a/drivers/clk/clk-scmi.c b/drivers/clk/clk-scmi.c
index 8cbe24789c24..4b6c43d7f5f3 100644
--- a/drivers/clk/clk-scmi.c
+++ b/drivers/clk/clk-scmi.c
@@ -2,9 +2,10 @@
 /*
  * System Control and Power Interface (SCMI) Protocol based clock driver
  *
- * Copyright (C) 2018-2022 ARM Ltd.
+ * Copyright (C) 2018-2024 ARM Ltd.
  */
 
+#include <linux/bits.h>
 #include <linux/clk-provider.h>
 #include <linux/device.h>
 #include <linux/err.h>
@@ -16,6 +17,13 @@
 #define NOT_ATOMIC	false
 #define ATOMIC		true
 
+enum scmi_clk_feats {
+	SCMI_CLK_ATOMIC_SUPPORTED,
+	SCMI_CLK_FEATS_COUNT
+};
+
+#define SCMI_MAX_CLK_OPS	BIT(SCMI_CLK_FEATS_COUNT)
+
 static const struct scmi_clk_proto_ops *scmi_proto_clk_ops;
 
 struct scmi_clk {
@@ -158,42 +166,6 @@ static int scmi_clk_atomic_is_enabled(struct clk_hw *hw)
 	return !!enabled;
 }
 
-/*
- * We can provide enable/disable/is_enabled atomic callbacks only if the
- * underlying SCMI transport for an SCMI instance is configured to handle
- * SCMI commands in an atomic manner.
- *
- * When no SCMI atomic transport support is available we instead provide only
- * the prepare/unprepare API, as allowed by the clock framework when atomic
- * calls are not available.
- *
- * Two distinct sets of clk_ops are provided since we could have multiple SCMI
- * instances with different underlying transport quality, so they cannot be
- * shared.
- */
-static const struct clk_ops scmi_clk_ops = {
-	.recalc_rate = scmi_clk_recalc_rate,
-	.round_rate = scmi_clk_round_rate,
-	.set_rate = scmi_clk_set_rate,
-	.prepare = scmi_clk_enable,
-	.unprepare = scmi_clk_disable,
-	.set_parent = scmi_clk_set_parent,
-	.get_parent = scmi_clk_get_parent,
-	.determine_rate = scmi_clk_determine_rate,
-};
-
-static const struct clk_ops scmi_atomic_clk_ops = {
-	.recalc_rate = scmi_clk_recalc_rate,
-	.round_rate = scmi_clk_round_rate,
-	.set_rate = scmi_clk_set_rate,
-	.enable = scmi_clk_atomic_enable,
-	.disable = scmi_clk_atomic_disable,
-	.is_enabled = scmi_clk_atomic_is_enabled,
-	.set_parent = scmi_clk_set_parent,
-	.get_parent = scmi_clk_get_parent,
-	.determine_rate = scmi_clk_determine_rate,
-};
-
 static int scmi_clk_ops_init(struct device *dev, struct scmi_clk *sclk,
 			     const struct clk_ops *scmi_ops)
 {
@@ -230,17 +202,129 @@ static int scmi_clk_ops_init(struct device *dev, struct scmi_clk *sclk,
 	return ret;
 }
 
+/**
+ * scmi_clk_ops_alloc() - Alloc and configure clock operations
+ * @dev: A device reference for devres
+ * @feats_key: A bitmap representing the desired clk_ops capabilities
+ *
+ * Allocate and configure a proper set of clock operations depending on the
+ * specifically required SCMI clock features.
+ *
+ * Return: A pointer to the allocated and configured clk_ops on success,
+ *	   or NULL on allocation failure.
+ */
+static const struct clk_ops *
+scmi_clk_ops_alloc(struct device *dev, unsigned long feats_key)
+{
+	struct clk_ops *ops;
+
+	ops = devm_kzalloc(dev, sizeof(*ops), GFP_KERNEL);
+	if (!ops)
+		return NULL;
+	/*
+	 * We can provide enable/disable/is_enabled atomic callbacks only if the
+	 * underlying SCMI transport for an SCMI instance is configured to
+	 * handle SCMI commands in an atomic manner.
+	 *
+	 * When no SCMI atomic transport support is available we instead provide
+	 * only the prepare/unprepare API, as allowed by the clock framework
+	 * when atomic calls are not available.
+	 */
+	if (feats_key & BIT(SCMI_CLK_ATOMIC_SUPPORTED)) {
+		ops->enable = scmi_clk_atomic_enable;
+		ops->disable = scmi_clk_atomic_disable;
+		ops->is_enabled = scmi_clk_atomic_is_enabled;
+	} else {
+		ops->prepare = scmi_clk_enable;
+		ops->unprepare = scmi_clk_disable;
+	}
+
+	/* Rate ops */
+	ops->recalc_rate = scmi_clk_recalc_rate;
+	ops->round_rate = scmi_clk_round_rate;
+	ops->determine_rate = scmi_clk_determine_rate;
+	ops->set_rate = scmi_clk_set_rate;
+
+	/* Parent ops */
+	ops->get_parent = scmi_clk_get_parent;
+	ops->set_parent = scmi_clk_set_parent;
+
+	return ops;
+}
+
+/**
+ * scmi_clk_ops_select() - Select a proper set of clock operations
+ * @sclk: A reference to an SCMI clock descriptor
+ * @atomic_capable: A flag to indicate if atomic mode is supported by the
+ *		    transport
+ * @atomic_threshold_us: Platform atomic threshold value in microseconds:
+ *			 clk_ops are atomic when clock enable latency is less
+ *			 than this threshold
+ * @clk_ops_db: A reference to the array used as a database to store all the
+ *		created clock operations combinations.
+ * @db_size: Maximum number of entries held by @clk_ops_db
+ *
+ * After having built a bitmap descriptor to represent the set of features
+ * needed by this SCMI clock, at first use it to lookup into the set of
+ * previously allocated clk_ops to check if a suitable combination of clock
+ * operations was already created; when no match is found allocate a brand new
+ * set of clk_ops satisfying the required combination of features and save it
+ * for future references.
+ *
+ * In this way only one set of clk_ops is ever created for each different
+ * combination that is effectively needed by a driver instance.
+ *
+ * Return: A pointer to the allocated and configured clk_ops on success, or
+ *	   NULL otherwise.
+ */
+static const struct clk_ops *
+scmi_clk_ops_select(struct scmi_clk *sclk, bool atomic_capable,
+		    unsigned int atomic_threshold_us,
+		    const struct clk_ops **clk_ops_db, size_t db_size)
+{
+	const struct scmi_clock_info *ci = sclk->info;
+	unsigned int feats_key = 0;
+	const struct clk_ops *ops;
+
+	/*
+	 * Note that when transport is atomic but SCMI protocol did not
+	 * specify (or support) an enable_latency associated with a
+	 * clock, we default to use atomic operations mode.
+	 */
+	if (atomic_capable && ci->enable_latency <= atomic_threshold_us)
+		feats_key |= BIT(SCMI_CLK_ATOMIC_SUPPORTED);
+
+	if (WARN_ON(feats_key >= db_size))
+		return NULL;
+
+	/* Lookup previously allocated ops */
+	ops = clk_ops_db[feats_key];
+	if (ops)
+		return ops;
+
+	/* Did not find a pre-allocated clock_ops */
+	ops = scmi_clk_ops_alloc(sclk->dev, feats_key);
+	if (!ops)
+		return NULL;
+
+	/* Store new ops combinations */
+	clk_ops_db[feats_key] = ops;
+
+	return ops;
+}
+
 static int scmi_clocks_probe(struct scmi_device *sdev)
 {
 	int idx, count, err;
-	unsigned int atomic_threshold;
-	bool is_atomic;
+	unsigned int atomic_threshold_us;
+	bool transport_is_atomic;
 	struct clk_hw **hws;
 	struct clk_hw_onecell_data *clk_data;
 	struct device *dev = &sdev->dev;
 	struct device_node *np = dev->of_node;
 	const struct scmi_handle *handle = sdev->handle;
 	struct scmi_protocol_handle *ph;
+	const struct clk_ops *scmi_clk_ops_db[SCMI_MAX_CLK_OPS] = {};
 
 	if (!handle)
 		return -ENODEV;
@@ -264,7 +348,8 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
 	clk_data->num = count;
 	hws = clk_data->hws;
 
-	is_atomic = handle->is_transport_atomic(handle, &atomic_threshold);
+	transport_is_atomic = handle->is_transport_atomic(handle,
+							  &atomic_threshold_us);
 
 	for (idx = 0; idx < count; idx++) {
 		struct scmi_clk *sclk;
@@ -286,15 +371,17 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
 		sclk->dev = dev;
 
 		/*
-		 * Note that when transport is atomic but SCMI protocol did not
-		 * specify (or support) an enable_latency associated with a
-		 * clock, we default to use atomic operations mode.
+		 * Note that the scmi_clk_ops_db is on the stack, not global,
+		 * because it cannot be shared between mulitple probe-sequences
+		 * to avoid sharing the devm_ allocated clk_ops between multiple
+		 * SCMI clk driver instances.
 		 */
-		if (is_atomic &&
-		    sclk->info->enable_latency <= atomic_threshold)
-			scmi_ops = &scmi_atomic_clk_ops;
-		else
-			scmi_ops = &scmi_clk_ops;
+		scmi_ops = scmi_clk_ops_select(sclk, transport_is_atomic,
+					       atomic_threshold_us,
+					       scmi_clk_ops_db,
+					       ARRAY_SIZE(scmi_clk_ops_db));
+		if (!scmi_ops)
+			return -ENOMEM;
 
 		/* Initialize clock parent data. */
 		if (sclk->info->num_parents > 0) {
@@ -318,8 +405,7 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
 		} else {
 			dev_dbg(dev, "Registered clock:%s%s\n",
 				sclk->info->name,
-				scmi_ops == &scmi_atomic_clk_ops ?
-				" (atomic ops)" : "");
+				scmi_ops->enable ? " (atomic ops)" : "");
 			hws[idx] = &sclk->hw;
 		}
 	}
-- 
2.44.0