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

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Date:	Wed, 6 Apr 2011 23:01:55 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	Michael Büsch <mb@...sch.de>
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

W dniu 6 kwietnia 2011 22:57 użytkownik Michael Büsch <mb@...sch.de> napisał:
> 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.

Sure, I've meant mutex inside bcmai (or whatever name), not on the driver side!

In BCMAI:
bcmai_read() {
mutex_get();
switch_core();
ioread();
mutex_release();
}

-- 
Rafał
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