linux-kernel - Re: [RFC 1/6] mailbox: add core framework

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Message-ID: <20140210190934.GA841@joshc.qualcomm.com>
Date:	Mon, 10 Feb 2014 13:09:34 -0600
From:	Josh Cartwright <joshc@...eaurora.org>
To:	Rob Herring <robherring2@...il.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Courtney Cavin <courtney.cavin@...ymobile.com>, s-anna@...com,
	Rob Herring <rob.herring@...xeda.com>,
	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
	Mark Langsdorf <mark.langsdorf@...xeda.com>,
	Tony Lindgren <tony@...mide.com>, omar.ramirez@...itl.com,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Rob Landley <rob@...dley.net>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 1/6] mailbox: add core framework

On Mon, Feb 10, 2014 at 11:52:05AM -0600, Rob Herring wrote:
> On Mon, Feb 10, 2014 at 8:11 AM, Arnd Bergmann <arnd@...db.de> wrote:
> > On Friday 07 February 2014 16:50:14 Courtney Cavin wrote:
[..]
> >> +int mbox_channel_notify(struct mbox_channel *chan,
> >> +             const void *data, unsigned int len)
> >> +{
> >> +     return atomic_notifier_call_chain(&chan->notifier, len, (void *)data);
> >> +}
> >> +EXPORT_SYMBOL(mbox_channel_notify);
> >
> > What is the reason to use a notifier chain here? Isn't a simple
> > callback function pointer enough? I would expect that each mailbox
> > can have exactly one consumer, not multiple ones.
> 
> It probably can be a callback, but there can be multiple consumers. It
> was only a notifier on the pl320 as there was no framework at the time
> and to avoid creating custom interfaces between drivers. On highbank
> for example, we can asynchronously receive the events for temperature
> change, power off, and reset. So either there needs to be an event
> demux somewhere or callbacks have to return whether they handled an
> event or not.

I'm not familiar with highbank IPC, but with these requirements should
the mailbox core even bother with asynchronous notifier chain?  It
sounds like a better fit might be for the mailbox core to implement a
proper adapter-specific irqdomain and used a chained irq handler to
demux (or have consumers request with IRQF_SHARED in the shared case).

-- 
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