netdev - Re: [PATCH 6/7] dt-bindings: net: bgmac: add bindings documentation for bgmac

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Date:	Fri, 01 Jul 2016 17:42:39 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Jon Mason <jon.mason@...adcom.com>
Cc:	Rafał Miłecki <zajec5@...il.com>,
	davem@...emloft.net, Florian Fainelli <f.fainelli@...il.com>,
	Hauke Mehrtens <hauke@...ke-m.de>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, Ray Jui <rjui@...adcom.com>,
	Scott Branden <sbranden@...adcom.com>,
	BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 6/7] dt-bindings: net: bgmac: add bindings documentation for bgmac

On Friday, July 1, 2016 11:17:25 AM CEST Jon Mason wrote:
> On Fri, Jul 1, 2016 at 5:46 AM, Arnd Bergmann <arnd@...db.de> wrote:
> > On Thursday, June 30, 2016 6:59:13 PM CEST Jon Mason wrote:
> >> +
> >> +Required properties:
> >> + - compatible: "brcm,bgmac-nsp"
> >> + - reg:                Address and length of the GMAC registers,
> >> +               Address and length of the GMAC IDM registers
> >> + - reg-names:  Names of the registers.  Must have both "gmac_base" and
> >> +               "idm_base"
> >> + - interrupts: Interrupt number
> >> +
> >
> >
> > "brcm,bgmac-nsp" sounds a bit too general. As I understand, this is a family
> > of SoCs that might not all have the exact same implementation of this
> > ethernet device, as we can see from the long lookup table in bgmac_probe().
> 
> The Broadcom iProc family of SoCs contains:
> Northstar
> Northstar Plus
> Cygnus
> Northstar 2
> a few SoCs that are under development
> and a number of ethernet switches (which might never be officially supported)
> 
> Each one of these SoCs could have a different revision of the gmac IP
> block, but they should be uniform within each SoC (though there might
> be a A0/B0 change necessary).  The Northstar Plus product family has a
> number of different implementations, but the SoC is unchanged.  So, I
> think this might be too specific, when we really need a general compat
> string.

Ok, thanks for the clarification, that sounds good enough.

> Broadcom has a history of sharing IP blocks amongst the different
> divisions.  So, this driver might be used on other SoC families (as it
> apparently has been done in the past, based on the code you
> reference).  I do not know of any way to know what legacy, non-iProc
> chips have used this IP block.  I can make this "brcm,iproc-bgmac",
> and add "brcm,iproc-nsp-bgmac" as an alternative compatible string in
> this file (which I believe you are suggesting), but there might be
> non-iProc SoCs that use this driver.  Is this acceptable?

If it is also used outside of iProc, then I see no need for the
extra compatible string, although it would not do any harm either.

Ideally we should name it whatever the name for this IP block is
inside of the company, with "nsp" as the designation for the variant
in Northstar Plus. A lot of Broadcom IP blocks themselves seem to have
some four-digit or five-digit number, maybe this one does too?

	Arnd