LOCAL / RFC / clk: Provide an always-on clock domain framework

Lots of platforms contain clocks which if turned off would prove fatal.
The only way to recover is to restart the board(s).  This driver takes
references to clocks which are required to be always-on in order to
prevent the common clk framework from trying to turn them off during
the clk_disabled_unused() procedure.

Signed-off-by: Lee Jones <lee.jones@linaro.org>

2 files changed, 74 insertions, 0 deletions

diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
index 3d00c25382c5..974dfcb7a4cd 100644
--- a/drivers/clk/Makefile
+++ b/drivers/clk/Makefile
@@ -3,6 +3,7 @@ obj-$(CONFIG_HAVE_CLK)		+= clk-devres.o
 obj-$(CONFIG_CLKDEV_LOOKUP)	+= clkdev.o
 obj-$(CONFIG_COMMON_CLK)	+= clk.o
 obj-$(CONFIG_COMMON_CLK)	+= clk-divider.o
+obj-$(CONFIG_COMMON_CLK)	+= clk-always-on.o
 obj-$(CONFIG_COMMON_CLK)	+= clk-fixed-factor.o
 obj-$(CONFIG_COMMON_CLK)	+= clk-fixed-rate.o
 obj-$(CONFIG_COMMON_CLK)	+= clk-gate.o
diff --git a/drivers/clk/clk-always-on.c b/drivers/clk/clk-always-on.c
new file mode 100644
index 000000000000..0e344975136b
--- /dev/null
+++ b/drivers/clk/clk-always-on.c
@@ -0,0 +1,73 @@
+/*
+ * Always-on Clock Domain
+ *
+ * Copyright (C) 2015 STMicroelectronics – All Rights Reserved
+ *
+ * Author: Lee Jones <lee.jones@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <linux/clk-provider.h>
+#include <linux/of_address.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+
+static void ao_clock_domain_hog_clock(struct platform_device *pdev, int index)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct clk *clk;
+	int ret;
+
+	clk = of_clk_get(np, index);
+	if (IS_ERR(clk)) {
+		dev_warn(&pdev->dev, "Failed get clock %s[%d]: %li\n",
+			 np->full_name, index, PTR_ERR(clk));
+		return;
+	}
+
+	ret = clk_prepare_enable(clk);
+	if (ret)
+		dev_warn(&pdev->dev, "Failed to enable clock: %s\n", __clk_get_name(clk));
+}
+
+static int ao_clock_domain_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	int nclks, i;
+
+	nclks = of_count_phandle_with_args(np, "clocks", "#clock-cells");
+
+	for (i = 0; i < nclks; i++)
+		ao_clock_domain_hog_clock(pdev, i);
+
+	return 0;
+}
+
+static const struct of_device_id ao_clock_domain_match[] = {
+	{ .compatible = "clk-always-on" },
+	{ },
+};
+
+static struct platform_driver ao_clock_domain_driver = {
+	.probe = ao_clock_domain_probe,
+	.driver = {
+		.name = "clk-always-on",
+		.of_match_table = ao_clock_domain_match,
+	},
+};
+
+static int __init ao_clock_domain_init(void)
+{
+	return platform_driver_register(&ao_clock_domain_driver);
+}
+arch_initcall(ao_clock_domain_init);
+
+static void __exit ao_clock_domain_exit(void)
+{
+	platform_driver_unregister(&ao_clock_domain_driver);
+}
+module_exit(ao_clock_domain_exit);