linux-kernel - Re: [PATCH v2 1/3] leds: add device activity LED triggers

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Date:	Fri, 2 Oct 2015 21:09:13 +0200
From:	Maciek Borzecki <maciek.borzecki@...il.com>
To:	Josh Cartwright <joshc@...com>
Cc:	linux-kernel@...r.kernel.org, Richard Purdie <rpurdie@...ys.net>,
	Jacek Anaszewski <j.anaszewski@...sung.com>,
	linux-leds@...r.kernel.org, linux-doc@...r.kernel.org,
	Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH v2 1/3] leds: add device activity LED triggers

On 10/02 12:08, Josh Cartwright wrote:
<snip>
>
> Hmm, maybe we're bikeshedding at this point, but LEDs with those names
> seem much more straightfoward to me than a "dev-<maj>:<min>" name, for
> devices which have done dynamic dev_t allocation.
>
> > Also, if I'm not mistaken, using this approach the partitions on MMC
> > card or SATA drive would end up with the same trigger name, as it is a
> > single device.
>
> This would only be true if you used _just_ the struct device.  I was
> imagining that you'd specify a (struct device, unsigned index) pair.
> Better, you could do a (struct device, const char *) pair.
>
> Also, from a lifetime management perspective, it starts to feel like
> something that might integrate better as a managed resource (devm_*).
>
> [..]
> > Multiple dev nodes will already have different minor numbers, so
> > their dev_t is different anyway.
>
> Okay, backing up I don't really see what this API really buys the
> consumer.  The dev_t -> struct led_trigger mapping just seems like a
> total waste.  Why not just make your ledtrig_dev_add() function return
> the struct led_trigger * that the consumer keeps track of?
>
> Maybe seeing an example consumer would provide some clarification.
>
> > As for devices that do not have a dev_t assigned to them one can still
> > pass a custom tag in ledtrig_dev_add(). It's just a number so as long as
> > there's no collision in numbering things should be fine.
>
> Ensuring no collision will be difficult, especially given that it's most
> common that the dynamic allocator is used.  In order to guarantee no
> collisions, a user who doesn't expose any device nodes would need to do
> their own dev_t allocation...to use this interface.  And that seems
> silly to me.

Thanks, I really appreciate your feedback.

--
Maciek Borzecki
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