Re: [PATCH 01/18] led-triggers: create a trigger for CPU activity

[Bryan Wu <bryan.wu@canonical.com>]

On Wed, Apr 18, 2012 at 6:52 AM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Tue, 17 Apr 2012 18:53:28 +0800
> Bryan Wu <bryan.wu@canonical.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@canonical.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.
>

OK, Fixed

>> 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>
>>
>
> A spurious newline.
>

OK, Fixed

>> Reviewed-by: Jamie Iles <jamie@jamieiles.com>
>> Tested-by: Jochen Friedrich <jochen@scram.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 ;))
>

Fixed

>> +       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.
>

"default N if (NR_CPUS > 9999)" isn't available, either.

>> +     /*
>> +      * Registering CPU led trigger for each CPU cores here
>
> s/cores/core/
>

Fixed

>> +      * 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?
>

If Richard has no objection, I will do this.

>> +             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@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)
>
> 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.
>
Fixed.

>> +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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-- 
Bryan Wu <bryan.wu@canonical.com>
Kernel Developer    +86.186-168-78255 Mobile
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