cpufreq: add sysfs interface

updates from previous versions: new sysfs_ops without "off" and "count", move the CONFIG_PROC_FS dependency of CONFIG_CPU_FREQ_PROC_INTF to Kconfig.

This patch adds a sysfs interface to the cpufreq core, and marks the previous /proc/cpufreq interface as deprecated.

As in drivers/base/cpu.c a "CPU driver" is registered, cpufreq acts as "interface" to this, offering the following files for each CPU (in /system/devices/sys/cpu.../) where CPUfreq support is present

cpuinfo_min_freq (ro) - minimum frequency (in kHz) the CPU supports
cpuinfo_max_freq (ro) - maximum frequency (in kHz) the CPU supports
scaling_min_freq (rw) - minimum frequency (in kHz) cpufreq may scale
the CPU core to
scaling_max_freq (rw) - maximum frequency (in kHz) cpufreq may scale
the CPU core to
scaling_governor (rw) - governor == "A feedback device on a machine
or engine that is used to provide automatic control, as of speed, pressure, or temperature" [1, as noted by David Kimdon]. Decides what frequency is used. Currently, only "performance" and "powersave" are supported, more may be added later.

(In future, a file scaling_driver (ro) which shows what CPUfreq driver is used (arm-sa1100, gx-suspmod, speedstep, longrun, powernow-k6, ...) might be added, and this driver will be allowed to add files scaling_driver_* for driver-specific settings like "prefer fast FSB". And scaling_governor_* files might offer settings for the governor.)

To implement this sysfs interface, the driver model "interface" code is used. Unfortunately, it has a non-trivial locking bug in drivers/base/intf.c: there's a down_write call for cls->subsys.rwsem in add_intf(), which then calls add(), which may call intf->add_device(), which may call interface_add_data(), which calls kobject_register(), which calls kobject_add(), which then tries to down_write cls->subsys.rwsem. Remember, that was already locked writable in add_intf().

Because of that, interface_add_data() is commented out; this means that no link in /system/class/cpu/cpufreq is added, and that the dev-removal code isn't called. This shouldn't be a problem yet, though; as no cpufreq driver I know of is capable of CPU hotplugging.

Dominik

[1] http://dictionary.reference.com/search?q=governor

diff -ruN linux-original/arch/i386/Kconfig linux/arch/i386/Kconfig
@@ -947,15 +947,27 @@
 
 	  If in doubt, say N.
 
+config CPU_FREQ_PROC_INTF
+	bool "/proc/cpufreq interface (DEPRECATED)"
+	depends on CPU_FREQ && PROC_FS
+	help
+	  This enables the /proc/cpufreq interface for controlling
+	  CPUFreq. Please note that it is recommended to use the sysfs
+	  interface instead (which is built automatically). 
+	  
+	  For details, take a look at linux/Documentation/cpufreq. 
+	  
+	  If in doubt, say N.
+
 config CPU_FREQ_24_API
 	bool "/proc/sys/cpu/ interface (2.4. / OLD)"
 	depends on CPU_FREQ
 	help
 	  This enables the /proc/sys/cpu/ sysctl interface for controlling
 	  CPUFreq, as known from the 2.4.-kernel patches for CPUFreq. 2.5
-	  uses /proc/cpufreq instead. Please note that some drivers do not 
-	  work well with the 2.4. /proc/sys/cpu sysctl interface, so if in
-	  doubt, say N here.
+	  uses a sysfs interface instead. Please note that some drivers do 
+	  not work well with the 2.4. /proc/sys/cpu sysctl interface,
+	  so if in doubt, say N here.
 
 	  For details, take a look at linux/Documentation/cpufreq. 
 

diff -ruN linux-original/include/linux/cpufreq.h linux/include/linux/cpufreq.h
@@ -17,6 +17,7 @@
 #include <linux/config.h>
 #include <linux/notifier.h>
 #include <linux/threads.h>
+#include <linux/device.h>
 
 
 /*********************************************************************

@@ -57,6 +58,7 @@
 	unsigned int            max;    /* in kHz */
         unsigned int            policy; /* see above */
 	struct cpufreq_cpuinfo  cpuinfo;     /* see above */
+	struct intf_data        intf;   /* interface data */
 };
 
 #define CPUFREQ_ADJUST          (0)