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Message-Id: <20120417155241.0f619a9a.akpm@linux-foundation.org>
Date: Tue, 17 Apr 2012 15:52:41 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Bryan Wu <bryan.wu@...onical.com>
Cc: linux@....linux.org.uk, rpurdie@...ys.net,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linus.walleij@...aro.org, arnd.bergmann@...aro.org,
nicolas.pitre@...aro.org, tim.gardner@...onical.com
Subject: Re: [PATCH 01/18] led-triggers: create a trigger for CPU activity
On Tue, 17 Apr 2012 18:53:28 +0800
Bryan Wu <bryan.wu@...onical.com> 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@...onical.com:
> It moves arch/arm/kernel/leds.c syscore stubs into this trigger.
No, the patch doesn't alter arch/arm/kernel/leds.c at all. This text
is either misleadingly phrased, or stale or something.
> 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@...ys.net>
> Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
> Signed-off-by: Bryan Wu <bryan.wu@...onical.com>
>
A spurious newline.
> Reviewed-by: Jamie Iles <jamie@...ieiles.com>
> Tested-by: Jochen Friedrich <jochen@...am.de>
>
> ...
>
> +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
s/what/which/ (I think ;))
> + CPUs are active on the system at any given moment.
> +
> + If unsure, say N.
> +
>
> ...
>
> +static int __init ledtrig_cpu_init(void)
> +{
> + int cpu;
> +
> + /* Supports up to 9999 cpu cores */
> + BUILD_BUG_ON(CONFIG_NR_CPUS > 9999);
hm, I wonder if this can be prevented in Kconfig logic. I guess
"depends on NR_CPUS <= 9999" isn't available.
> + /*
> + * Registering CPU led trigger for each CPU cores here
s/cores/core/
> + * 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);
> + struct rw_semaphore *lock = &per_cpu(trig_lock, cpu);
> +
> + init_rwsem(lock);
> +
> + snprintf(name, MAX_NAME_LEN, "cpu%d", cpu);
> +
> + down_write(lock);
> + led_trigger_register_simple(name, &trig);
OK, problem.
led_trigger_register_simple() calls kzalloc() and
led_trigger_register(), both of which can fail.
led_trigger_register_simple() just returns void, failing to propagate
the error back. This is bad, and we (ie you ;)) should fix
led_trigger_register_simple() before proceeding to use it. If at all
possible. Please. Let us not propagate the badness further. Sorry.
> + per_cpu(cpu_trig, cpu) = trig;
> + up_write(lock);
> + }
> +
> + register_syscore_ops(&ledtrig_cpu_syscore_ops);
> +
> + pr_info("ledtrig-cpu: registered to indicate activity on CPUs\n");
> +
> + 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);
grr. drivers/leds/led-triggers.c sometimes does
struct led_trigger trigger;
and sometimes
struct led_trigger trig;
which makes the code needlessly more difficult to follow. So if you're
fiddling with drivers/leds/led-triggers.c, please fix that up - use
"trig" everywhere?
> + char *name = per_cpu(trig_name, cpu);
> +
> + led_trigger_unregister_simple(trig);
And what happens if led_trigger_register_simple() had silently failed
to register this trigger? afacit, nothing: your code handles the
trig==NULL case OK. Still, we should be checking for those failures!
> + 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@...aro.org>");
> +MODULE_AUTHOR("Bryan Wu <bryan.wu@...onical.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)
See lkml subject "RFC: strip 15,000 lines from a typical autoconf.h".
We might be able to simplify this. But the above is OK for now.
> +/**
> + * 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.
> + */
It's conventional to add kerneldoc at the function definition site, not
at the declaration. Nobody thinks to look in the .h file for
documentation.
> +extern void ledtrig_cpu(enum cpu_led_event evt);
> +#else
> +static inline void ledtrig_cpu(enum cpu_led_event evt)
> +{
> + return;
> +}
> +#endif
> +
--
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