[PATCH v3 0/2] add specified-clock DT binding

[PATCH v3 0/2] add specified-clock DT binding

[James Hogan]

Resurrecting a year old patchset I'm still interested in, which I didn't
get any review comments for with v2.

The frequency of some fixed rate external oscillators on some SoCs (for
example TZ1090's XTAL1) are specified by the board using pull-ups and
pull-downs of configuration pins which are automatically latched on
reset and available in an SoC register, so that the boot ROM and OS can
automatically discover it.

The first patch adds a separate binding for these clocks to describe how
to discover the frequency. I could easily have extended the fixed-rate
binding instead, but there'd be no properties in common except the
standard common clock properties so it seemed like it deserved a
separate binding. I'm open to arguments to the contrary or better
compatible string names though.

The second patch implements the binding, which sets up a normal fixed
rate clock just like the normal fixed-clock binding except it discovers
the frequency instead of using the clock-frequency property.

Changes in v3:
 * Remove unused & unimplemented gpios property. Not sure why it was
   there in the first place.

Changes in v2:
 * Split out bindings patch for ease of review.
 * Rewrite to use a fixed clock instead of an entirely new clock type.
 * Borrow bit-mask and bit-shift bindings from Mike's mux clock binding
   proposals.

James Hogan (2):
  dt: binding: add specified-clock for discoverable rate clocks
  clk-fixed-rate: support specified-clock binding

 .../devicetree/bindings/clock/specified-clock.txt  | 37 ++++++++++++++++
 drivers/clk/clk-fixed-rate.c                       | 51 ++++++++++++++++++++++
 include/linux/clk-provider.h                       |  1 +
 3 files changed, 89 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/clock/specified-clock.txt

-- 
2.0.4

[PATCH v3 1/2] dt: binding: add specified-clock for discoverable rate clocks

[James Hogan]

The frequency of some fixed rate external oscillators on some SoCs (for
example TZ1090's XTAL1) are specified by the board using pull-ups and
pull-downs of configuration pins which are automatically latched on
reset and available in an SoC register, so that the boot ROM and OS can
automatically discover it.

These clocks are very similar to fixed-clocks since the rate never
changes, but we still want to be able to automatically discover the
frequency, so add a new binding to describe such clocks. Instead of
using a "clock-frequency" property, use "reg", "bit-mask", "bit-shift"
properties to describe the register field. The mapping from register
values to clock frequencies is specified in a "table" property which
contains pairs of register values and frequencies.

There is scope to extend the binding further in future to handle other
mapping types, by using different properties instead of "table".

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Mike Turquette <mturquette@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: devicetree@vger.kernel.org
---
Changes in v3:
 * Remove unused & unimplemented gpios property. Not sure why it was
   there in the first place.

I could easily have extended the fixed-rate binding instead, but there'd
be no properties in common except the standard common clock properties
so it seemed like it deserved a separate binding. I'm open to arguments
to the contrary or better compatible string names though.

Changes in v2:
 * Borrow bit-mask and bit-shift bindings from Mike's mux clock binding
   proposals.
---
 .../devicetree/bindings/clock/specified-clock.txt  | 37 ++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/clock/specified-clock.txt

diff --git a/Documentation/devicetree/bindings/clock/specified-clock.txt b/Documentation/devicetree/bindings/clock/specified-clock.txt
new file mode 100644
index 0000000..4a8e5d3
--- /dev/null
+++ b/Documentation/devicetree/bindings/clock/specified-clock.txt
@@ -0,0 +1,37 @@
+Binding for discoverable-fixed-rate clock sources.
+
+This binding uses the common clock binding[1].
+
+[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
+
+Required properties:
+- compatible : shall be "specified-clock".
+- #clock-cells : from common clock binding; shall be set to 0.
+- reg : Base address of configuration register specifying the frequency.
+- bit-mask : Mask of bits in the field specifying the frequency.
+- table : array of integer pairs defining register field values and
+  corresponding clock frequencies in Hz.
+
+Optional properties:
+- bit-shift : Number of bits to shift the masked register value,
+  defaults to (ffs(bit-mask) - 1) if absent.
+- clock-output-names : From common clock binding.
+
+Example:
+	clock {
+		compatible = "specified-clock";
+		#clock-cells = <0>;
+		reg = <0x02004004 0x4>;		/* CR_PERIP_RESET_CFG */
+		bit-mask = <0x00000f00>;	/* FXTAL */
+		table =	/*	FXTAL	Frequency */
+				<0	16384000>,
+				<1	19200000>,
+				<2	24000000>,
+				<3	24576000>,
+				<4	26000000>,
+				<5	36000000>,
+				<6	36864000>,
+				<7	38400000>,
+				<8	40000000>;
+		clock-output-names = "xtal1";
+	};
-- 
2.0.4

[PATCH v3 2/2] clk-fixed-rate: support specified-clock binding

[James Hogan]

Implement the new specified-clock DT binding which uses a table to look
up the fixed frequency based on the value in a register.

The discovery is done entirely within of_specified_clk_setup() since the
clock rate is still fixed so there's no need to dynamically rediscover
the rate. The register is iomapped, read, and iounmapped, then the field
value is extracted and used to look up the clock frequency in the table
property.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Mike Turquette <mturquette@linaro.org>
---
No changes in v3.

Changes in v2:
 * Rewrite to use a fixed clock instead of an entirely new clock type.
---
 drivers/clk/clk-fixed-rate.c | 51 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/clk-provider.h |  1 +
 2 files changed, 52 insertions(+)

diff --git a/drivers/clk/clk-fixed-rate.c b/drivers/clk/clk-fixed-rate.c
index 0fc56ab..b8bcb4d 100644
--- a/drivers/clk/clk-fixed-rate.c
+++ b/drivers/clk/clk-fixed-rate.c
@@ -9,12 +9,14 @@
  * Fixed rate clock implementation
  */
 
+#include <linux/bitops.h>
 #include <linux/clk-provider.h>
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/io.h>
 #include <linux/err.h>
 #include <linux/of.h>
+#include <linux/of_address.h>
 
 /*
  * DOC: basic fixed-rate clock that cannot gate
@@ -134,4 +136,53 @@ void of_fixed_clk_setup(struct device_node *node)
 }
 EXPORT_SYMBOL_GPL(of_fixed_clk_setup);
 CLK_OF_DECLARE(fixed_clk, "fixed-clock", of_fixed_clk_setup);
+
+/**
+ * of_specified_clk_setup() - Setup function for discoverable fixed rate clock
+ */
+void of_specified_clk_setup(struct device_node *node)
+{
+	struct clk *clk;
+	const char *clk_name = node->name;
+	u32 shift, mask, rate, reg_val, val;
+	void __iomem *reg;
+	struct property *prop;
+	const __be32 *p;
+
+	/* Iomap and read the configuration register */
+	reg = of_iomap(node, 0);
+	if (!reg)
+		return;
+	reg_val = readl(reg);
+	iounmap(reg);
+
+	/* Apply bit-mask */
+	if (of_property_read_u32(node, "bit-mask", &mask))
+		return;
+	reg_val &= mask;
+	/* Apply bit-shift */
+	if (of_property_read_u32(node, "bit-shift", &shift))
+		shift = ffs(mask) - 1;
+	reg_val >>= shift;
+
+	/* Look through the mapping for a matching frequency */
+	of_property_for_each_u32(node, "table", prop, p, val) {
+		p = of_prop_next_u32(prop, p, &rate);
+		if (!p)
+			break;
+		if (val == reg_val)
+			goto found_rate;
+	}
+	/* No match found */
+	return;
+found_rate:
+
+	of_property_read_string(node, "clock-output-names", &clk_name);
+
+	clk = clk_register_fixed_rate(NULL, clk_name, NULL, CLK_IS_ROOT, rate);
+	if (!IS_ERR(clk))
+		of_clk_add_provider(node, of_clk_src_simple_get, clk);
+}
+EXPORT_SYMBOL_GPL(of_specified_clk_setup);
+CLK_OF_DECLARE(specified_clk, "specified-clock", of_specified_clk_setup);
 #endif
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index be21af1..7e5c1d3 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -257,6 +257,7 @@ struct clk *clk_register_fixed_rate_with_accuracy(struct device *dev,
 		unsigned long fixed_rate, unsigned long fixed_accuracy);
 
 void of_fixed_clk_setup(struct device_node *np);
+void of_specified_clk_setup(struct device_node *np);
 
 /**
  * struct clk_gate - gating clock
-- 
2.0.4