linux-kernel - Re: [RFC/PATCH 1/5] usb: otg: add notifier support

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Message-ID: <20100126131146.GC32291@sirena.org.uk>
Date:	Tue, 26 Jan 2010 13:11:47 +0000
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	David Brownell <david-b@...bell.net>
Cc:	Felipe Balbi <felipe.balbi@...ia.com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Anton Vorontsov <avorontsov@...mvista.com>,
	Grazvydas Ignotas <notasas@...il.com>,
	Madhusudhan Chikkature <madhu.cr@...com>,
	linux-omap@...r.kernel.org, Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [RFC/PATCH 1/5] usb: otg: add notifier support

On Tue, Jan 26, 2010 at 03:16:20AM -0800, David Brownell wrote:

> I'd vote to convert all the USB-to-charger interfaces so
> they use notifiers.  After fixing the events ... see
> comments below.  :)

Yes please - it's not just chargers either, this can also be used by
PMICs which do power path management that includes USB.

> Those seem like the wrong events.  The right events for a charger
> would be more along the lines of:

>  - For peripheral:  "you may use N milliAmperes now".
>  - General:  "Don't Charge" (a.k.a. "use 0 mA").

> I don't see how "N" would be passed with those events ...

These are good for the peripheral side.  You do get to pass a void *
along with the notifier value, that could be used to pass data like the
current limit.

> A host *might* want to be able to say things like "supply
> up to N milliAmperes now", e.g. to let a regulator choose
> the most efficient mode.

Yes, they definitely want this - not just for efficiency but also to
allow current limiting to protect the system from excessive current
drain.
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