[PATCH RFC 3/5] clk: bcm281xx: implement prerequisite clocks

[Artur Weber <aweber.kernel@gmail.com>]

From: Alex Elder <elder@kernel.org>

Allow a clock to specify a "prerequisite" clock, identified by its
name.  The prerequisite clock must be prepared and enabled before a
clock that depends on it is used.  In order to simplify locking, we
require a clock and its prerequisite to be associated with the same
CCU.  (We'll just trust--but not verify--that nobody defines a cycle
of prerequisite clocks.)

Rework the KONA_CLK() macro, and define a new KONA_CLK_PREREQ()
variant that allows a prerequisite clock to be specified.

Signed-off-by: Alex Elder <elder@linaro.org>
--- Artur: rebase on v6.13, move prereq prepare/unprepare to main
    prepare/unprepare functions, use locking versions of clk_prepare
    and clk_enable since the non-locking versions are no longer
    public ---
Signed-off-by: Artur Weber <aweber.kernel@gmail.com>
---
 drivers/clk/bcm/clk-kona.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++
 drivers/clk/bcm/clk-kona.h | 20 ++++++++++++---
 2 files changed, 79 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/bcm/clk-kona.c b/drivers/clk/bcm/clk-kona.c
index e92d57f3bbb147e72221802175a80502897d7504..21f925683d0da05ebc97f92236dfb207b1f9c741 100644
--- a/drivers/clk/bcm/clk-kona.c
+++ b/drivers/clk/bcm/clk-kona.c
@@ -9,6 +9,7 @@
 #include <linux/delay.h>
 #include <linux/io.h>
 #include <linux/kernel.h>
+#include <linux/clk.h>
 #include <linux/clk-provider.h>
 
 /*
@@ -961,6 +962,63 @@ static int selector_write(struct ccu_data *ccu, struct bcm_clk_gate *gate,
 	return ret;
 }
 
+/*
+ * Common clock prepare/unprepare functions. These implement a "prerequisite"
+ * mechanism; the prerequisite clock is prepared and enabled before the main
+ * clock is prepared.
+ */
+
+static int kona_clk_prepare(struct clk_hw *hw)
+{
+	struct kona_clk *bcm_clk = to_kona_clk(hw);
+	const char *clk_name = bcm_clk->init_data.name;
+	const char *prereq_name = bcm_clk->prereq.name;
+	struct clk *prereq_clk = bcm_clk->prereq.clk;
+	int ret;
+
+	/* If there's no prerequisite clock, there's nothing to do */
+	if (!prereq_name)
+		return 0;
+
+	/* Look up the prerequisite clock if we haven't already */
+	if (!prereq_clk) {
+		prereq_clk = __clk_lookup(prereq_name);
+		if (WARN_ON_ONCE(!prereq_clk))
+			return -ENOENT;
+		bcm_clk->prereq.clk = prereq_clk;
+	}
+
+	ret = clk_prepare(prereq_clk);
+	if (ret) {
+		pr_err("%s: unable to prepare prereq clock %s for %s\n",
+			__func__, prereq_name, clk_name);
+		return ret;
+	}
+
+	ret = clk_enable(prereq_clk);
+	if (ret) {
+		clk_unprepare(prereq_clk);
+		pr_err("%s: unable to enable prereq clock %s for %s\n",
+			__func__, prereq_name, clk_name);
+		return ret;
+	}
+
+	return 0;
+}
+
+static void kona_clk_unprepare(struct clk_hw *hw)
+{
+	struct kona_clk *bcm_clk = to_kona_clk(hw);
+	struct clk *prereq_clk = bcm_clk->prereq.clk;
+
+	/* If there's no prerequisite clock, there's nothing to do */
+	if (!bcm_clk->prereq.name)
+		return;
+
+	clk_disable(prereq_clk);
+	clk_unprepare(prereq_clk);
+}
+
 /* Peripheral clock operations */
 
 static int kona_peri_clk_enable(struct clk_hw *hw)
@@ -1172,6 +1230,8 @@ static int kona_peri_clk_set_rate(struct clk_hw *hw, unsigned long rate,
 }
 
 struct clk_ops kona_peri_clk_ops = {
+	.prepare = kona_clk_prepare,
+	.unprepare = kona_clk_unprepare,
 	.enable = kona_peri_clk_enable,
 	.disable = kona_peri_clk_disable,
 	.is_enabled = kona_peri_clk_is_enabled,
@@ -1260,6 +1320,8 @@ static int kona_bus_clk_is_enabled(struct clk_hw *hw)
 }
 
 struct clk_ops kona_bus_clk_ops = {
+	.prepare = kona_clk_prepare,
+	.unprepare = kona_clk_unprepare,
 	.enable = kona_bus_clk_enable,
 	.disable = kona_bus_clk_disable,
 	.is_enabled = kona_bus_clk_is_enabled,
diff --git a/drivers/clk/bcm/clk-kona.h b/drivers/clk/bcm/clk-kona.h
index a5b3d8bdb54eaee9fad80c28796170207b817dfd..c32c621282ec6dd40fff3f7598ee8aa007fed524 100644
--- a/drivers/clk/bcm/clk-kona.h
+++ b/drivers/clk/bcm/clk-kona.h
@@ -406,6 +406,10 @@ struct kona_clk {
 	struct clk_init_data init_data;	/* includes name of this clock */
 	struct ccu_data *ccu;	/* ccu this clock is associated with */
 	enum bcm_clk_type type;
+	struct {
+		const char *name;
+		struct clk *clk;
+	} prereq;
 	union {
 		void *data;
 		struct peri_clk_data *peri;
@@ -416,16 +420,26 @@ struct kona_clk {
 	container_of(_hw, struct kona_clk, hw)
 
 /* Initialization macro for an entry in a CCU's kona_clks[] array. */
-#define KONA_CLK(_ccu_name, _clk_name, _type)				\
-	{								\
+#define __KONA_CLK_COMMON(_ccu_name, _clk_name, _type)			\
 		.init_data	= {					\
 			.name = #_clk_name,				\
 			.ops = &kona_ ## _type ## _clk_ops,		\
 		},							\
 		.ccu		= &_ccu_name ## _ccu_data,		\
 		.type		= bcm_clk_ ## _type,			\
-		.u.data		= &_clk_name ## _data,			\
+		.u.data		= &_clk_name ## _data
+
+#define KONA_CLK(_ccu_name, _clk_name, _type)				\
+	{								\
+		__KONA_CLK_COMMON(_ccu_name, _clk_name, _type),	\
 	}
+
+#define KONA_CLK_PREREQ(_ccu_name, _clk_name, _type, _prereq)		\
+	{								\
+		.prereq.name	= #_prereq,				\
+		__KONA_CLK_COMMON(_ccu_name, _clk_name, _type),	\
+	}
+
 #define LAST_KONA_CLK	{ .type = bcm_clk_none }
 
 /*

-- 
2.48.1