linux-kernel - Re: [RFC][PATCH] bcmai: introduce AI driver

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Date:	Wed, 06 Apr 2011 22:57:08 +0200
From:	Michael Büsch <mb@...sch.de>
To:	Rafał Miłecki <zajec5@...il.com>
Cc:	Arend van Spriel <arend@...adcom.com>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"John W. Linville" <linville@...driver.com>,
	Larry Finger <Larry.Finger@...inger.net>,
	George Kashperko <george@...u.edu.ua>,
	"b43-dev@...ts.infradead.org" <b43-dev@...ts.infradead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King <rmk@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	linuxdriverproject <devel@...uxdriverproject.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] bcmai: introduce AI driver

On Wed, 2011-04-06 at 22:42 +0200, Rafał Miłecki wrote: 
> 2011/4/6 Rafał Miłecki <zajec5@...il.com>:
> > If we want to have two drivers working on two (different) cores
> > simultaneously, we will have to add trivial mutex to group core
> > switching with core operation (read/write).
> 
> With a little of work we could avoid switching and mutexes on no-host
> boards. MMIO is not limited to one core at once in such a case.

I don't think that this is a problem at all.
All that magic does happen inside of the bus I/O handlers.
Just like SSB does it.
>From a driver point of view, the I/O functions just need to
be atomic.

For SSB it's not always 100% atomic, but we're always safe
due to some assumptions being made. But this is an SSB implementation
detail that is different from AXI. So don't look too closely
at the SSB implementation of the I/O functions. You certainly want
to implement them slightly differently in AXI. SSB currently doesn't
make use of the additional sliding windows, because they are not
available in the majority of SSB devices.

The AXI bus subsystem will manage the sliding windows and the driver
doesn't know about the details.

-- 
Greetings Michael.

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