[PATCH 2/3] clk: Introduce 'critical-clocks' property

[Marek Vasut <marex@denx.de>]

Some platforms require clock to be always running, e.g. because those clock
supply devices which are not otherwise attached to the system. One example
is a system where the SoC serves as a crystal oscillator replacement for a
programmable logic device. The critical-clock property of a clock controller
allows listing clock which must never be turned off.

The implementation here is similar to "protected-clock", except protected
clock property is currently driver specific. This patch attempts to make
a generic implementation of "critical-clock" instead.

Unlike "assigned-clocks", the "critical-clock" must be parsed much earlier
in __clk_register() to assign CLK_IS_CRITICAL flag to clk_init_data .flags
field. The parsing code obviously need to be cleaned up and factor out into
separate function.

The new match_clkspec() callback is used to determine whether struct clk_hw
that is currently being registered matches the clock specifier in the DT
"critical-clock" property, and if so, then the CLK_IS_CRITICAL is added to
these newly registered clock. This callback is currently driver specific,
although I suspect a common and/or generic version of the callback could
be added. Also, this new callback could possibly be used to replace (*get)
argument of of_clk_add_hw_provider() later on too.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: devicetree@vger.kernel.org
Cc: linux-power@fi.rohmeurope.com
To: linux-clk@vger.kernel.org
---
 drivers/clk/clk.c            | 41 ++++++++++++++++++++++++++++++++++++
 include/linux/clk-provider.h |  3 +++
 2 files changed, 44 insertions(+)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 8de6a22498e70..1e1686fa76e01 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -3872,6 +3872,45 @@ static void clk_core_free_parent_map(struct clk_core *core)
 	kfree(core->parents);
 }
 
+static void
+__clk_register_critical_clock(struct device_node *np, struct clk_core *core,
+			      struct clk_hw *hw)
+{
+	struct of_phandle_args clkspec;
+	u32 clksize, clktotal;
+	int ret, i, index;
+
+	if (!np)
+		return;
+
+	if (!core->ops->match_clkspec)
+		return;
+
+	if (of_property_read_u32(np, "#clock-cells", &clksize))
+		return;
+
+	/* Clock node with #clock-cells = <0> uses critical-clocks; */
+	if (clksize == 0) {
+		if (of_property_read_bool(np, "critical-clocks") &&
+		    !core->ops->match_clkspec(hw, &clkspec))
+			core->flags |= CLK_IS_CRITICAL;
+		return;
+	}
+
+	clkspec.np = np;
+	clktotal = of_property_count_u32_elems(np, "critical-clocks");
+	clktotal /= clksize;
+	for (index = 0; index < clktotal; index++) {
+		for (i = 0; i < clksize; i++) {
+			ret = of_property_read_u32_index(np, "critical-clocks",
+							 (index * clksize) + i,
+							 &(clkspec.args[i]));
+		}
+		if (!core->ops->match_clkspec(hw, &clkspec))
+			core->flags |= CLK_IS_CRITICAL;
+	}
+}
+
 static struct clk *
 __clk_register(struct device *dev, struct device_node *np, struct clk_hw *hw)
 {
@@ -3916,6 +3955,8 @@ __clk_register(struct device *dev, struct device_node *np, struct clk_hw *hw)
 	core->min_rate = 0;
 	core->max_rate = ULONG_MAX;
 
+	__clk_register_critical_clock(np, core, hw);
+
 	ret = clk_core_populate_parent_map(core, init);
 	if (ret)
 		goto fail_parents;
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index 2faa6f7aa8a87..8bc0eedfeb2fd 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -205,6 +205,8 @@ struct clk_duty {
  *		directory is provided as an argument.  Called with
  *		prepare_lock held.  Returns 0 on success, -EERROR otherwise.
  *
+ * @match_clkspec: Check whether clk_hw matches DT clock specifier.
+ *		Returns 0 on success, -EERROR otherwise.
  *
  * The clk_enable/clk_disable and clk_prepare/clk_unprepare pairs allow
  * implementations to split any work between atomic (enable) and sleepable
@@ -252,6 +254,7 @@ struct clk_ops {
 	int		(*init)(struct clk_hw *hw);
 	void		(*terminate)(struct clk_hw *hw);
 	void		(*debug_init)(struct clk_hw *hw, struct dentry *dentry);
+	int		(*match_clkspec)(struct clk_hw *hw, struct of_phandle_args *clkspec);
 };
 
 /**
-- 
2.34.1