linux-kernel - Re: [PATCH v3 1/8] rsb: Add generic Reduced Serial Bus (RSB) controller binding documentation

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Message-ID: <20150820212446.GK30520@lukather>
Date:	Thu, 20 Aug 2015 23:24:46 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Chen-Yu Tsai <wens@...e.org>
Cc:	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>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Brown <broonie@...nel.org>,
	devicetree <devicetree@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-sunxi <linux-sunxi@...glegroups.com>,
	Hans de Goede <hdegoede@...hat.com>,
	Meng Zhang <kevin@...winnertech.com>,
	Shuge <shuge@...winnertech.com>,
	Meng Zhang <kevin.z.m.zh@...il.com>
Subject: Re: [PATCH v3 1/8] rsb: Add generic Reduced Serial Bus (RSB)
 controller binding documentation

On Thu, Aug 20, 2015 at 11:58:39PM +0800, Chen-Yu Tsai wrote:
> >> +Child nodes:
> >> +
> >> +An RSB controller node can contain zero or more child nodes representing
> >> +slave devices on the bus.  Child 'reg' properties are specified as a
> >> +runtime address, hardware address pair. The hardware address is hardwired
> >> +in the device, which can normally be found in the datasheet. The runtime
> >> +address is set by software. No 2 devices on the same bus shall have the
> >> +same runtime address.
> >> +
> >> +Valid runtime addresses - There are only 15 valid runtime addresses:
> >> +
> >> +    0x17, 0x2d, 0x3a, 0x4e, 0x59, 0x63, 0x74, 0x8b,
> >> +    0x9c, 0xa6, 0xb1, 0xc5, 0xd2, 0xe8, 0xff
> >> +
> >> +It is highly recommended that one choose the same runtime addresses as
> >> +vendor BSPs use so that a) the addresses remain the same across different
> >> +software systems, and b) addresses of supported and listed slave devices
> >> +don't conflict with unsupported or not yet listed devices.
> >
> > I'd expect to have the hardware address first, but maybe it's just me
> > :)
> 
> I don't know. It's only used at init time.
> 
> And in my latest experience, once the runtime address is set by the
> bootloader, it can't be changed. My earlier experience was the opposite,
> though I haven't figured out why.

Note that I'm only talking about the order of runtime and hardware
addresses in the reg property, having both is fine.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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