linux-kernel - Re: ledtrig-cpu: Limit to 4 CPUs

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Message-ID: <20200921224212.GA13299@amd>
Date:   Tue, 22 Sep 2020 00:42:12 +0200
From:   Pavel Machek <pavel@....cz>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     linux-leds@...r.kernel.org, dmurphy@...com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: ledtrig-cpu: Limit to 4 CPUs

Hi!

> >Can I get details of your setup?
> 
> I don't use this trigger, but I can imagine that someone does.

Well, if someone exists, we can increase the limit, or convince them
to change their setup.

> >What CPU type that is, and how are you mapping CPU activity to LEDs?
> 
> The type of CPU is irrelevant here. What is important is the fact
> that with this trigger it is possible to visually monitor CPU core
> online state. Probably it would be good to ask the author of that
> trigger about his use case.

It is relevant -- cpu trigger never worked on x86. I had patch fixing
it, but got pushback.

> I have spoken up, because I don't get the reason for your patch.
> This driver was reworked year ago to remove PAGE_SIZE limit,
> and I even applied it to my for-next tree, but that was at
> the time of handling maintainership to yourself, and you
> seem to not have picked that commit.
> 
> Was that intentional? We had even Greg's ack [0].

I checked, and I believe the commit is in:

#ifdef CONFIG_LEDS_TRIGGERS
static BIN_ATTR(trigger, 0644, led_trigger_read, led_trigger_write,
0);
static struct bin_attribute *led_trigger_bin_attrs[] = {

So.. no, it is not causing kernel crashes or something. But it is
example of bad interface, and _that_ is causing problems. (And yes, if
I realized it is simply possible to limit it, maybe the BIN_ATTR
conversion would not be neccessary...)

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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