linux-kernel - Re: Could I (ab)use bus (struct bus

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Date:	Fri, 15 Apr 2011 22:42:21 +0300
From:	George Kashperko <george@...u.edu.ua>
To:	Rafał Miłecki <zajec5@...il.com>
Cc:	Hauke Mehrtens <hauke@...ke-m.de>,
	Russell King <rmk@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	linux-wireless@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Arend van Spriel <arend@...adcom.com>,
	Jonas Gorski <jonas.gorski@...il.com>,
	b43-dev@...ts.infradead.org, Greg KH <greg@...ah.com>,
	Andy Botting <andy@...ybotting.com>,
	Larry Finger <Larry.Finger@...inger.net>
Subject: Re: Could I (ab)use bus (struct bus_type) for virtual Broadcom bus?


> W dniu 15 kwietnia 2011 20:36 użytkownik George Kashperko
> <george@...u.edu.ua> napisał:
> >> >> Arnd: I found you saying:
> >> >> > I believe the one thing we really want from this driver is the bus
> >> >> > scan code, which is not present in the amba bus implementation,
> >> >> I explained how it works, I believe scanning (EPROM in this case) it
> >> >> Broadcom specific, not really AMBA standard. How do you see it?
> >> >>
> >> > It might not Broadcom specific as EPROM core seems to be CoreLink one
> >> > core and maybe is arm-developed. But it isn't documented publicly and we
> >> > don't know yet if it is obligatory for all amba (or at least axi)
> >> > interconnects or not.
> >>
> >> Maybe EPROM is not Broadcom specific, but I suspect the content we
> >> deal with in bcmai/axi is Broadcom specific. I didn't see any notes of
> >> manuf/id/rev/class we deal with. So I guess everything *we* (out
> >> driver) read from EPROM is Bcm specific.
> >>
> >
> > Played around amba registers on bcm4716. For all amba cores present
> > (under all I mean broadcom ip core agents, oob router core, erom core,
> > and other I-dont-know-what-for cores present at 0x18100000). All those
> > feature AMBA_CID (0xb105f00d) as PrimeCell ID, and slightly different
> > PrimeCell PeripheralIDs:
> > * vendor 0xBB, part_number 0x368 for broadcom cores' agents;
> > * vendor 0xBB, part_number 0x367 for OOB router core (don't ask me wth
> > is this please);
> > * vendor 0xBB, part_number 0x366 for EROM core;
> >
> > ARM vendor id is 0x41. Might 0xBB is Broadcom vendor id but I've found
> > no evidence for that with google.
> 
> Yeah, as I suspected, everything except Broadcom specific cores
> matches AMBA standards quite nicely. Still, I don't see anything in it
> we could use for driver.
> 
> Let's wait for Russell and Arnd to comment.

Summarising the differences and similarities in broadcom core management
for ssb and amba I think on another possibility on making bus-related
things.
SSB-attached cores were OCP-compliant ones. This resulted in OCP device
identification with 16-bit vendor id, 12-bit core id with all IDs
starting with 0x800. 4-bit revision code. Also seems this implied
status/control registers.
AMBA-attached broadcom cores seems to follow this reusing their
OCP-compliant cores on axi.

So, we could start with introducing virtual "ocp" bus (which could be of
some use for other vendors utilising ocp model) with additional
library/module for broadcom-specific extensions (accounting for
buscommon/buscore/etc.).

On other hand just broadcom-specific bus looks like good alternative too
but here I just fail to decide on relevant naming.

Have nice day,
George


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