Date:	Wed, 28 Jan 2009 20:20:07 +0100
From:	Davide Rizzo <elpa.rizzo@...il.com>
To:	Greg KH <gregkh@...e.de>
Cc:	"Hans J. Koch" <hjk@...utronix.de>, linux-kernel@...r.kernel.org,
	ben-linux@...ff.org, linux-api@...r.kernel.org
Subject: Re: [PATCH 1/3] Driver for user access to internal clocks

> Same comments here as for your "timer.c" file:
>        - too generic of a name
>        - needs proper documentation
>        - send any kernel api changes also to linux-api@...r.kernel.org
>
> thanks,
>
> greg k-h
>
Here is the modified user mode clock access driver.
I moved it in /drivers/misc and reorganized virtual files under /sys/class/clock

This driver is for user level programs to interact with system clocks.
It allows to read and modify rates and parents, using virtual files.
It requires the implementation of 2 additional functions in the clk interface:
 clk_for_each() and clk_name().
Actually I implemented that functions only for Samsung S3C24xx platform.

Signed-off-by: Davide Rizzo <elpa.rizzo@...il.com>
---
diff -urpN linux-2.6.29-rc2/drivers/misc/Kconfig
linux-2.6.29-rc2.elpa/drivers/misc/Kconfig
--- linux-2.6.29-rc2/drivers/misc/Kconfig	2009-01-17 11:32:40.000000000 +0100
+++ linux-2.6.29-rc2.elpa/drivers/misc/Kconfig	2009-01-28
19:21:43.000000000 +0100
@@ -232,4 +232,19 @@ config DELL_LAPTOP

 source "drivers/misc/c2port/Kconfig"

+config UM_CLOCK
+	bool "User mode clock driver"
+	depends on SYSFS
+	default n
+	---help---
+	Allows user mode programs to configure and control internal clocks'
+	 rates and parents through virtual files in sysfs.
+	This driver requires implementation of some additional functions
+	 in architecture specific low-level drivers: clk_for_each() and
+	 clk_get_name(). Moreover, it requires clk_get() to recognize the
+	 "name.id" format
+	Currently they're implemented only on Samsung S3C24xx platforms.
+
+	If unsure, say N.
+
 endif # MISC_DEVICES
diff -urpN linux-2.6.29-rc2/drivers/misc/Makefile
linux-2.6.29-rc2.elpa/drivers/misc/Makefile
--- linux-2.6.29-rc2/drivers/misc/Makefile	2009-01-17 11:32:40.000000000 +0100
+++ linux-2.6.29-rc2.elpa/drivers/misc/Makefile	2009-01-28
19:21:43.000000000 +0100
@@ -20,3 +20,4 @@ obj-$(CONFIG_SGI_XP)		+= sgi-xp/
 obj-$(CONFIG_SGI_GRU)		+= sgi-gru/
 obj-$(CONFIG_HP_ILO)		+= hpilo.o
 obj-$(CONFIG_C2PORT)		+= c2port/
+obj-$(CONFIG_UM_CLOCK) += um_clock.o
diff -urpN linux-2.6.29-rc2/drivers/misc/um_clock.c
linux-2.6.29-rc2.elpa/drivers/misc/um_clock.c
--- linux-2.6.29-rc2/drivers/misc/um_clock.c	1970-01-01 01:00:00.000000000 +0100
+++ linux-2.6.29-rc2.elpa/drivers/misc/um_clock.c	2009-01-28
19:21:43.000000000 +0100
@@ -0,0 +1,174 @@
+/*
+ driver/misc/clock.c
+
+ Written Feb 2008 by Davide Rizzo <elpa.rizzo@...il.com>
+
+ This driver allows to read and modify internal clocks' rates using
+  virtual files. User can also read and modify parents.
+
+ This driver requires implementation of clk_name() and clk_enum() functions
+  in architecture specific clock.c
+
+ 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.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software
+ Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+*/
+
+#include <linux/device.h>
+#include <linux/clk.h>
+#include <linux/kdev_t.h>
+#include <linux/err.h>
+
+static DEFINE_MUTEX(mutex);
+
+static ssize_t rate_show(struct device *dev, struct device_attribute *attr,
+	char *buffer)
+{
+	unsigned long rate;
+	struct clk *clk;
+
+	clk = dev_get_drvdata(dev);
+	rate = 0;
+
+	mutex_lock(&mutex);
+
+	rate = clk_get_rate(clk);
+
+	mutex_unlock(&mutex);
+
+	return sprintf(buffer, "%ld\n", rate);
+}
+
+static ssize_t rate_store(struct device *dev, struct device_attribute *attr,
+	const char *buffer, size_t count)
+{
+	unsigned long rate;
+	struct clk *clk;
+	int err;
+
+	clk = dev_get_drvdata(dev);
+	err = strict_strtoul(buffer, 10, &rate);
+	if (err)
+		return err;
+
+	mutex_lock(&mutex);
+
+	if (rate != 0) {
+		clk_set_rate(clk, clk_round_rate(clk, rate));
+		clk_enable(clk);
+	} else
+		clk_disable(clk);
+
+	mutex_unlock(&mutex);
+
+	return count;
+}
+
+static ssize_t parent_show(struct device *dev,
+	struct device_attribute *attr, char *buffer)
+{
+	struct clk *parent, *clk;
+
+	clk = dev_get_drvdata(dev);
+
+	mutex_lock(&mutex);
+
+	parent = clk_get_parent(clk);
+	if (parent && !IS_ERR(parent)) {
+		const char *name = clk_get_name(parent);
+		if (IS_ERR(name)) {
+			mutex_unlock(&mutex);
+			return PTR_ERR(name);
+		}
+		strlcpy(buffer, name, PAGE_SIZE);
+	} else
+		buffer[0] = '\0';
+	strlcat(buffer, "\n", PAGE_SIZE);
+
+	mutex_unlock(&mutex);
+
+	return strlen(buffer);
+}
+
+static ssize_t parent_store(struct device *dev,
+	struct device_attribute *attr, const char *buffer, size_t count)
+{
+	struct clk *parent;
+
+	char *s = kstrdup(buffer, GFP_KERNEL);
+
+	if (!s)
+		return -ENOMEM;
+	if (s[strlen(s) - 1] == '\n')
+		s[strlen(s) - 1] = '\0';
+	parent = clk_get(dev, s);
+	kfree(s);
+	if (IS_ERR(parent))
+		return PTR_ERR(parent);
+
+	mutex_lock(&mutex);
+
+	clk_set_parent(dev_get_drvdata(dev), parent);
+
+	mutex_unlock(&mutex);
+
+	clk_put(parent);
+	return count;
+}
+
+static DEVICE_ATTR(rate, S_IRUGO | S_IWUSR, rate_show, rate_store);
+static DEVICE_ATTR(parent, S_IRUGO | S_IWUSR, parent_show, parent_store);
+
+static const struct attribute *clock_attrs[] = {
+	&dev_attr_rate.attr,
+	&dev_attr_parent.attr,
+	NULL,
+};
+
+static const struct attribute_group clock_attr_group = {
+	.attrs = (struct attribute **) clock_attrs,
+};
+
+static struct class gpclock_class = {
+	.name =		"clock",
+	.owner =	THIS_MODULE,
+};
+
+static int create_clock_attr(struct clk *clk, void *data)
+{
+	struct device *dev;
+	const char *name;
+
+	name = clk_get_name(clk);
+	if (name == NULL || IS_ERR(name)) {
+		pr_debug("Invalid clock's name\n");
+		return PTR_ERR(name);
+	}
+	dev = device_create(&gpclock_class, (struct device *)data, MKDEV(0, 0),
+		clk, name);
+	if (!dev)
+		return -ENODEV;
+	return sysfs_create_group(&dev->kobj, &clock_attr_group);
+}
+
+static int __init gpclock_init(void)
+{
+	int ret;
+
+	ret = class_register(&gpclock_class);
+	if (ret >= 0)
+		ret = clk_for_each(create_clock_attr, NULL);
+	return ret;
+}
+subsys_initcall(gpclock_init);
+
diff -urpN linux-2.6.29-rc2/Documentation/ABI/testing/sysfs-class-clock
linux-2.6.29-rc2.elpa/Documentation/ABI/testing/sysfs-class-clock
--- linux-2.6.29-rc2/Documentation/ABI/testing/sysfs-class-clock	1970-01-01
01:00:00.000000000 +0100
+++ linux-2.6.29-rc2.elpa/Documentation/ABI/testing/sysfs-class-clock	2009-01-28
19:21:43.000000000 +0100
@@ -0,0 +1,20 @@
+What:		/sys/class/clock
+Date:		January 2009
+Contact:	Davide Rizzo <elpa.rizzo@...il.com>
+Description:
+		The /sys/class/clock directory will consist of a group of
+		subdirectories each one describing an internal clock in the kernel.
+		The name of the subdirectory is the clock's name.
+		If a clock is device specific, its name is in the form "name.id".
+		In each directory there are 2 virtual files: rate and parent.
+		Both these files are r/w, but there can be some architecture-dependent
+		limitations on write access on one or both of them.
+		For this interface to work, it needs some low-level implementations (look
+		at include/linux/clk.h):
+		- clk_for_each()
+		- clk_name()
+		- clk_get() should recognize also the "name.id" format
+		Actually I implemented these only for Samsung S3C SoC in
+		arch/arm/plat-s3c/clock.c
+
+Users:
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