linux-kernel - Re: [PATCH 2/2] drivers/amba: probe via device tree

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Date:	Mon, 23 May 2011 09:09:41 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Kristoffer Glembo <kristoffer@...sler.com>,
	Kevin Hilman <khilman@...com>,
	Stephen Neuendorffer <stephen.neuendorffer@...inx.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	devicetree-discuss@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] drivers/amba: probe via device tree

On Mon, May 23, 2011 at 3:58 AM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Mon, May 23, 2011 at 11:37:04AM +0200, Kristoffer Glembo wrote:
>> Grant Likely wrote:
>> > In the case we're talking about the bus really is an AMBA bus, and all
>> > the devices on it are in some sense real amba devices.  The problem is
>> > that not all of the devices on the bus implement peripheral ID
>> > registers or other mechanisms that good upstanding AMBA devices are
>> > expected to have.
>>
>> Before we go hardware bashing of non primecell AMBA devices I would just
>> want to point out that the primecell stuff is not part of the AMBA
>> specification.
>
> And before we go down that route, let me point out that the 'amba bus'
> stuff in the kernel is there to support primecells, rather than all
> devices which the AMBA specification covers.
>
> The reason it's called 'amba' is because back in 2001 or so when the
> first primecell drivers were created, there was little information
> available as to what AMBA, AHB, or APB even covered.  All I had to go
> on were the primecell documents themselves.  The higher level documents
> were not available to me.
>
> So, despite it being called 'amba', it really is just for primecells
> and if we didn't have the exposure to userspace, I'd have renamed it to
> 'apb' or similar instead.

Okay, that clarifies things a lot, and lends weight to the arguement
that it is perfectly normal and acceptable to have both amba_devices
and platform_devices on the same bus segment.  Are there any cases
where amba primecells are being driven by platform_drivers?  If so,
should those drivers have an amba_driver registration added?

g.
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