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

Artur Weber
2025-02-16T16:12:53Z

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