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    SubjectRe: [PATCH 01/18] led-triggers: create a trigger for CPU activity
    On 04/13/2012 05:26 AM, Bryan Wu wrote:
    > Attempting to consolidate the ARM LED code, this removes the
    > custom RealView LED trigger code to turn LEDs on and off in
    > response to CPU activity and replace it with a standard trigger.
    >
    > (bryan.wu@canonical.com:
    > It moves arch/arm/kernel/leds.c syscore stubs into this trigger.
    > It also provides ledtrig_cpu trigger event stub in <linux/leds.h>.
    > Although it was inspired by ARM work, it can be used in other arch.)
    >
    > Cc: Richard Purdie <rpurdie@rpsys.net>
    > Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
    > Signed-off-by: Bryan Wu <bryan.wu@canonical.com>
    >
    > Reviewed-by: Jamie Iles <jamie@jamieiles.com>
    > Tested-by: Jochen Friedrich <jochen@scram.de>
    > ---
    > drivers/leds/Kconfig | 10 ++++
    > drivers/leds/Makefile | 1 +
    > drivers/leds/ledtrig-cpu.c | 133 ++++++++++++++++++++++++++++++++++++++++++++
    > include/linux/leds.h | 23 ++++++++
    > 4 files changed, 167 insertions(+)
    > create mode 100644 drivers/leds/ledtrig-cpu.c
    >
    > diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
    > index 9f2b8dd..6e445a0 100644
    > --- a/drivers/leds/Kconfig
    > +++ b/drivers/leds/Kconfig
    > @@ -457,6 +457,16 @@ config LEDS_TRIGGER_BACKLIGHT
    >
    > If unsure, say N.
    >
    > +config LEDS_TRIGGER_CPU
    > + tristate "LED CPU Trigger"
    > + depends on LEDS_TRIGGERS
    > + help
    > + This allows LEDs to be controlled by active CPUs. This shows
    > + the active CPUs across an array of LEDs so you can see what
    > + CPUs are active on the system at any given moment.
    > +
    > + If unsure, say N.
    > +
    > config LEDS_TRIGGER_GPIO
    > tristate "LED GPIO Trigger"
    > depends on LEDS_TRIGGERS
    > diff --git a/drivers/leds/Makefile b/drivers/leds/Makefile
    > index 14481cf..8bb20e6 100644
    > --- a/drivers/leds/Makefile
    > +++ b/drivers/leds/Makefile
    > @@ -55,4 +55,5 @@ obj-$(CONFIG_LEDS_TRIGGER_IDE_DISK) += ledtrig-ide-disk.o
    > obj-$(CONFIG_LEDS_TRIGGER_HEARTBEAT) += ledtrig-heartbeat.o
    > obj-$(CONFIG_LEDS_TRIGGER_BACKLIGHT) += ledtrig-backlight.o
    > obj-$(CONFIG_LEDS_TRIGGER_GPIO) += ledtrig-gpio.o
    > +obj-$(CONFIG_LEDS_TRIGGER_CPU) += ledtrig-cpu.o
    > obj-$(CONFIG_LEDS_TRIGGER_DEFAULT_ON) += ledtrig-default-on.o
    > diff --git a/drivers/leds/ledtrig-cpu.c b/drivers/leds/ledtrig-cpu.c
    > new file mode 100644
    > index 0000000..52ef19c
    > --- /dev/null
    > +++ b/drivers/leds/ledtrig-cpu.c
    > @@ -0,0 +1,133 @@
    > +/*
    > + * ledtrig-cpu.c - LED trigger based on CPU activity
    > + *
    > + * This LED trigger will be registered for each possible CPU and named as
    > + * cpu0, cpu1, cpu2, cpu3, etc.
    > + *
    > + * It can be binded with any LEDs as other triggers does, either in board
    > + * file or via sysfs interface.
    > + *

    "It can be bound to any LED just like other triggers using either a
    board file or via sysfs interface."

    > + * An API named ledtrig_cpu is exported for any user, who want to add CPU
    > + * activity indication in their code
    > + *
    > + * Copyright 2011 Linus Walleij <linus.walleij@linaro.org>
    > + * Copyright 2011 - 2012 Bryan Wu <bryan.wu@canonical.com>
    > + *
    > + * 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.
    > + *
    > + */
    > +
    > +#include <linux/module.h>
    > +#include <linux/kernel.h>
    > +#include <linux/init.h>
    > +#include <linux/slab.h>
    > +#include <linux/percpu.h>
    > +#include <linux/syscore_ops.h>
    > +#include "leds.h"
    > +
    > +#define MAX_NAME_LEN 8
    > +

    This length accommodates up to 10000 CPUs. How long will that suffice ?

    > +static DEFINE_PER_CPU(struct led_trigger *, cpu_trig);
    > +static DEFINE_PER_CPU(char [MAX_NAME_LEN], trig_name);
    > +
    > +void ledtrig_cpu(enum cpu_led_event ledevt)
    > +{
    > + struct led_trigger *trig = __get_cpu_var(cpu_trig);
    > +
    > + if (!trig)
    > + return;

    I don't think __get_cpu_var(cpu_trig) _should_ ever return NULL. See
    discussion about exclusion below in ledtrig_cpu_init().

    > +
    > + /* Locate the correct CPU LED */
    > + switch (ledevt) {
    > + case CPU_LED_IDLE_END:
    > + case CPU_LED_START:
    > + /* Will turn the LED on, max brightness */
    > + led_trigger_event(trig, LED_FULL);
    > + break;
    > +
    > + case CPU_LED_IDLE_START:
    > + case CPU_LED_STOP:
    > + case CPU_LED_HALTED:
    > + /* Will turn the LED off */
    > + led_trigger_event(trig, LED_OFF);
    > + break;
    > +
    > + default:
    > + /* Will leave the LED as it is */
    > + break;
    > + }
    > +}
    > +EXPORT_SYMBOL(ledtrig_cpu);
    > +
    > +static int ledtrig_cpu_syscore_suspend(void)
    > +{
    > + ledtrig_cpu(CPU_LED_STOP);
    > + return 0;
    > +}
    > +
    > +static void ledtrig_cpu_syscore_resume(void)
    > +{
    > + ledtrig_cpu(CPU_LED_START);
    > +}
    > +
    > +static void ledtrig_cpu_syscore_shutdown(void)
    > +{
    > + ledtrig_cpu(CPU_LED_HALTED);
    > +}
    > +
    > +static struct syscore_ops ledtrig_cpu_syscore_ops = {
    > + .shutdown = ledtrig_cpu_syscore_shutdown,
    > + .suspend = ledtrig_cpu_syscore_suspend,
    > + .resume = ledtrig_cpu_syscore_resume,
    > +};
    > +
    > +static int __init ledtrig_cpu_init(void)
    > +{
    > + int cpu;
    > +
    > + /*
    > + * Registering CPU led trigger for each CPU cores here
    > + * ignores CPU hotplug, but after this CPU hotplug works
    > + * fine with this trigger.
    > + */
    > + for_each_possible_cpu(cpu) {
    > + struct led_trigger *trig;
    > + char *name = per_cpu(trig_name, cpu);
    > +
    > + snprintf(name, MAX_NAME_LEN, "cpu%d", cpu);
    > + led_trigger_register_simple(name, &trig);

    Check for trig == NULL. led_trigger_register_simple() does a
    kzalloc(GFP_KERNEL). You'll also have to unwind any successful
    registrations. Perhaps carve the guts out of ledtrig_cpu_exit() into a
    function that can be called from either place.

    Furthermore, I think there is a race here. As soon as
    led_trigger_register_simple() has completed, then the trigger is
    available for use. Won't you need some kind of exclusion to block
    consumers before trig is assigned ? There is a similar problem in
    ledtrig_cpu().

    > + per_cpu(cpu_trig, cpu) = trig;
    > +
    > + pr_info("LED trigger %s indicate activity on CPU %d\n",
    > + trig->name, cpu);

    This seems like an unnecessary log filler, especially as the number of
    CPUs becomes large. How about just a single line after the loop completes ?

    > + }
    > +
    > + register_syscore_ops(&ledtrig_cpu_syscore_ops);
    > +
    > + return 0;
    > +}
    > +module_init(ledtrig_cpu_init);
    > +
    > +static void __exit ledtrig_cpu_exit(void)
    > +{
    > + int cpu;
    > +
    > + for_each_possible_cpu(cpu) {
    > + struct led_trigger *trig = per_cpu(cpu_trig, cpu);
    > + char *name = per_cpu(trig_name, cpu);
    > +
    > + led_trigger_unregister_simple(trig);
    > + per_cpu(cpu_trig, cpu) = NULL;
    > + memset(name, 0, MAX_NAME_LEN);
    > + }
    > +
    > + unregister_syscore_ops(&ledtrig_cpu_syscore_ops);
    > +}
    > +module_exit(ledtrig_cpu_exit);
    > +
    > +MODULE_AUTHOR("Linus Walleij <linus.walleij@linaro.org>");
    > +MODULE_AUTHOR("Bryan Wu <bryan.wu@canonical.com>");
    > +MODULE_DESCRIPTION("CPU LED trigger");
    > +MODULE_LICENSE("GPL");
    > diff --git a/include/linux/leds.h b/include/linux/leds.h
    > index 5884def..1215b94 100644
    > --- a/include/linux/leds.h
    > +++ b/include/linux/leds.h
    > @@ -210,4 +210,27 @@ struct gpio_led_platform_data {
    > struct platform_device *gpio_led_register_device(
    > int id, const struct gpio_led_platform_data *pdata);
    >
    > +enum cpu_led_event {
    > + CPU_LED_IDLE_START, /* CPU enters idle */
    > + CPU_LED_IDLE_END, /* CPU idle ends */
    > + CPU_LED_START, /* Machine starts, especially resume */
    > + CPU_LED_STOP, /* Machine stops, especially suspend */
    > + CPU_LED_HALTED, /* Machine shutdown */
    > +};
    > +#if defined(CONFIG_LEDS_TRIGGER_CPU) || defined(CONFIG_LEDS_TRIGGER_CPU_MODULE)
    > +/**
    > + * ledtrig_cpu - emit a CPU event as a trigger
    > + * @evt: CPU event to be emitted
    > + *
    > + * Emit a CPU event on a CPU core, which will trigger a
    > + * binded LED to turn on or turn off.
    > + */
    > +extern void ledtrig_cpu(enum cpu_led_event evt);
    > +#else
    > +static inline void ledtrig_cpu(enum cpu_led_event evt)
    > +{
    > + return;
    > +}
    > +#endif
    > +
    > #endif /* __LINUX_LEDS_H_INCLUDED */


    --
    Tim Gardner tim.gardner@canonical.com

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