[PATCH v2] clk: Add PWM clock driver

[Philipp Zabel <p.zabel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>]

Some board designers, when running out of clock output pads, decide to
(mis)use PWM output pads to provide a clock to external components.
This driver supports this practice by providing an adapter between the
PWM and clock bindings in the device tree. As the PWM bindings specify
the period in the device tree, this is a fixed clock.

Signed-off-by: Philipp Zabel <p.zabel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
---
I'm resending this because last time the linux-pwm list was not in Cc:
So far I have not received any comments on the patch itself. I have used
it on a BoundaryDevices Nitrogen6X board to produce a master clock for
the OV5640 MIPI CSI-2 camera module.

Changes since v1:
 - none (rebased onto v3.18-rc3)
---
 .../devicetree/bindings/clock/pwm-clock.txt        |  23 +++++
 drivers/clk/Kconfig                                |   7 ++
 drivers/clk/Makefile                               |   1 +
 drivers/clk/clk-pwm.c                              | 110 +++++++++++++++++++++
 4 files changed, 141 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/clock/pwm-clock.txt
 create mode 100644 drivers/clk/clk-pwm.c

diff --git a/Documentation/devicetree/bindings/clock/pwm-clock.txt b/Documentation/devicetree/bindings/clock/pwm-clock.txt
new file mode 100644
index 0000000..d127d17
--- /dev/null
+++ b/Documentation/devicetree/bindings/clock/pwm-clock.txt
@@ -0,0 +1,23 @@
+Binding for an external clock signal driven by a PWM pin.
+
+This binding uses the common clock binding[1] and the common PWM binding[2].
+
+[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
+[2] Documentation/devicetree/bindings/pwm/pwm.txt
+
+Required properties:
+- compatible : shall be "pwm-clock".
+- #clock-cells : from common clock binding; shall be set to 0.
+- pwms : from common PWM binding; this determines the clock frequency
+  via the PWM period given in the pwm-specifier.
+
+Optional properties:
+- clock-output-names : From common clock binding.
+
+Example:
+	clock {
+		compatible = "pwm-clock";
+		#clock-cells = <0>;
+		clock-output-names = "mipi_mclk";
+		pwms = <&pwm2 0 40>; /* 1 / 40 ns = 25 MHz */
+	};
diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
index 455fd17..36a6918a 100644
--- a/drivers/clk/Kconfig
+++ b/drivers/clk/Kconfig
@@ -129,6 +129,13 @@ config COMMON_CLK_PALMAS
 	  This driver supports TI Palmas devices 32KHz output KG and KG_AUDIO
 	  using common clock framework.
 
+config COMMON_CLK_PWM
+	bool "Clock driver for PWMs used as clock outputs"
+	depends on PWM
+	---help---
+	  Adapter driver so that any PWM output can be (mis)used as clock signal
+	  at 50% duty cycle.
+
 config COMMON_CLK_PXA
 	def_bool COMMON_CLK && ARCH_PXA
 	---help---
diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
index d5fba5b..6a0c5cf 100644
--- a/drivers/clk/Makefile
+++ b/drivers/clk/Makefile
@@ -40,6 +40,7 @@ obj-$(CONFIG_ARCH_U300)			+= clk-u300.o
 obj-$(CONFIG_ARCH_VT8500)		+= clk-vt8500.o
 obj-$(CONFIG_COMMON_CLK_WM831X)		+= clk-wm831x.o
 obj-$(CONFIG_COMMON_CLK_XGENE)		+= clk-xgene.o
+obj-$(CONFIG_COMMON_CLK_PWM)		+= clk-pwm.o
 obj-$(CONFIG_COMMON_CLK_AT91)		+= at91/
 obj-$(CONFIG_ARCH_BCM_MOBILE)		+= bcm/
 obj-$(CONFIG_ARCH_BERLIN)		+= berlin/
diff --git a/drivers/clk/clk-pwm.c b/drivers/clk/clk-pwm.c
new file mode 100644
index 0000000..8f747b3
--- /dev/null
+++ b/drivers/clk/clk-pwm.c
@@ -0,0 +1,110 @@
+/*
+ * Copyright (C) 2014 Philipp Zabel, Pengutronix
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * PWM (mis)used as clock output
+ */
+#include <linux/clk-provider.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+
+struct clk_pwm {
+	struct clk_hw hw;
+	struct pwm_device *pwm;
+};
+
+#define to_clk_pwm(_hw) container_of(_hw, struct clk_pwm, hw)
+
+static int clk_pwm_enable(struct clk_hw *hw)
+{
+	struct clk_pwm *clk_pwm = to_clk_pwm(hw);
+
+	return pwm_enable(clk_pwm->pwm);
+}
+
+static void clk_pwm_disable(struct clk_hw *hw)
+{
+	struct clk_pwm *clk_pwm = to_clk_pwm(hw);
+
+	pwm_disable(clk_pwm->pwm);
+}
+
+static unsigned long clk_pwm_recalc_rate(struct clk_hw *hw,
+					 unsigned long parent_rate)
+{
+	struct clk_pwm *clk_pwm = to_clk_pwm(hw);
+	unsigned int period_ns = pwm_get_period(clk_pwm->pwm);
+
+	return period_ns ? (1000000000 / period_ns) : 0;
+}
+
+const struct clk_ops clk_pwm_ops = {
+	.enable = clk_pwm_enable,
+	.disable = clk_pwm_disable,
+	.recalc_rate = clk_pwm_recalc_rate,
+};
+
+int clk_pwm_probe(struct platform_device *pdev)
+{
+	struct clk_init_data init;
+	struct clk_pwm *clk_pwm;
+	struct pwm_device *pwm;
+	struct clk *clk;
+	int ret;
+
+	clk_pwm = devm_kzalloc(&pdev->dev, sizeof(*clk_pwm), GFP_KERNEL);
+	if (!clk_pwm)
+		return -ENOMEM;
+
+	pwm = devm_pwm_get(&pdev->dev, NULL);
+	if (IS_ERR(pwm))
+		return PTR_ERR(pwm);
+
+	ret = pwm_config(pwm, (pwm->period + 1) >> 1, pwm->period);
+	if (ret < 0)
+		return ret;
+
+	init.name = "pwm-clock";
+	init.ops = &clk_pwm_ops;
+	init.flags = CLK_IS_ROOT;
+	init.num_parents = 0;
+
+	clk_pwm->pwm = pwm;
+	clk_pwm->hw.init = &init;
+	clk = devm_clk_register(&pdev->dev, &clk_pwm->hw);
+	if (IS_ERR(clk))
+		return PTR_ERR(clk);
+
+	return of_clk_add_provider(pdev->dev.of_node,
+				   of_clk_src_simple_get, clk);
+}
+
+int clk_pwm_remove(struct platform_device *pdev)
+{
+	of_clk_del_provider(pdev->dev.of_node);
+
+	return 0;
+}
+
+static const struct of_device_id clk_pwm_dt_ids[] = {
+	{ .compatible = "pwm-clock" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, clk_pwm_dt_ids);
+
+static struct platform_driver clk_pwm_driver = {
+	.probe = clk_pwm_probe,
+	.driver = {
+		.name = "pwm-clock",
+		.owner = THIS_MODULE,
+		.of_match_table = of_match_ptr(clk_pwm_dt_ids),
+	},
+};
+
+module_platform_driver(clk_pwm_driver);
-- 
2.1.1

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