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

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Message-ID: <BANLkTim30i8kBkvsSvmWxQaNxWkfMjhOZA@mail.gmail.com>
Date:	Thu, 7 Apr 2011 11:55:03 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	Michael Büsch <mb@...sch.de>
Cc:	George Kashperko <george@...u.edu.ua>,
	Arnd Bergmann <arnd@...db.de>,
	Russell King <rmk@....linux.org.uk>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"b43-dev@...ts.infradead.org" <b43-dev@...ts.infradead.org>,
	Arend van Spriel <arend@...adcom.com>,
	linuxdriverproject <devel@...uxdriverproject.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Larry Finger <Larry.Finger@...inger.net>
Subject: Re: [RFC][PATCH] bcmai: introduce AI driver

W dniu 7 kwietnia 2011 09:54 użytkownik Michael Büsch <mb@...sch.de> napisał:
> On Thu, 2011-04-07 at 02:54 +0200, Rafał Miłecki wrote:
>> W dniu 7 kwietnia 2011 02:00 użytkownik George Kashperko
>> <george@...u.edu.ua> napisał:
>> > For PCI function description take a look at PCI specs or PCI
>> > configuration space description (e. g.
>> > http://en.wikipedia.org/wiki/PCI_configuration_space)
>> >
>> > Sorry for missleading short-ups, w11 - bcm80211 core, under two-head I
>> > mean ssb/axi with two functional cores on same interconnect (like w11
>> > +w11, not a lot of these exists I guess). Also there were some b43+b44
>> > on single PCI ssb host and those where implemented as ssb interconnect
>> > on multifunctional PCI host therefore providing separate access windows
>> > for each function.
>> >
>> > Might I mussunderstood something (its late night here at my place) when
>> > you where talking about using coreswitching involved for two drivers
>> > therefore I remembered about those functions. Seems now you were talking
>> > about chipcommon+b43 access sharing same window.
>> >
>> > As for core switching requirments for earlier SSB interconnects on PCI
>> > hosts where there were no direct chipcommon access, that one can be
>> > accomplished without spin_lock/mutex for b43 or b44 cores with proper
>> > bus design.
>> >
>> > AXI doesn't need spinlocks/mutexes as both chipcommon and pci bridge are
>> > available directly and b43 will be the only one requiring window access.
>>
>> Ahh, so while talking about 4 windows, I guess you counted fixes
>> windows as well. That would be right, matching my knowledge.
>>
>> When asking question about amount of cores we may want to use
>> simultaneously I didn't think about ChipCommon or PCIe. The real
>> problem would be to support for example two 802.11 cores and one
>> ethernet core at the same time. That gives us 3 cores while we have
>> only 2 sliding windows.
>
> Would that really be a problem? Think of it. This combination
> will only be available on embedded devices. But do we have windows
> on embedded devices? I guess not. If AXI is similar to SSB, the MMIO
> of all cores will always be mapped. So accesses can be done
> without switch or lock.
>
> I do really think that engineers at broadcom are clever enough
> to design a hardware that does not require expensive window sliding
> all the time while operating.

I also think so. When asking about amount of cores (non PCIe, non
ChipCommon) which has to work simultaneously. I'm not sure if we will
meet AI board with 2 cores (non PCIe, non ChipCommon) on PCIe host. I
don't think we will see more than 2 cores (non PCIe, non ChipCommon)
on PCIe host.

-- 
Rafał
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