linux-kernel - RE: [PATCH 1/5 v2] Add the explanation and a sample of RapidIO DTS sector to the document of booting-without-of.txt file.

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Message-ID: <46B96294322F7D458F9648B60E15112C6F3312@zch01exm26.fsl.freescale.net>
Date:	Fri, 29 Jun 2007 17:20:27 +0800
From:	"Zhang Wei-r63237" <Wei.Zhang@...escale.com>
To:	"Segher Boessenkool" <segher@...nel.crashing.org>
Cc:	<linux-kernel@...r.kernel.org>, <mporter@...nel.crashing.org>,
	<paulus@...ba.org>, <linuxppc-dev@...abs.org>
Subject: RE: [PATCH 1/5 v2] Add the explanation and a sample of RapidIO DTS sector to the document of booting-without-of.txt file.

Hi, Segher, 

> DTS sector to the document of booting-without-of.txt file.
> 
> >>> +    - #address-cells : Address representation for
> >> "rapidio" devices.
> >>> +      This field represents the number of cells needed 
> to represent
> >>> +      the RapidIO address of the registers.  For
> >> supporting more than
> >>> +      32-bits RapidIO address, this field should be <2>.
> >>> +      See 1) above for more details on defining #address-cells.
> >>
> >> What does the RapidIO standard say about number of address
> >> bits?  You want to follow that, so all RapidIO devices can
> >> use the same #address-cells, not just the FSL ones.  Also,
> >> are there different kinds of address spaces on the bus, or
> >> is it just one big memory-like space?
> >
> > I've checked the specification of RapidIO. The supporting of RapidIO
> > extended address modes are 66, 50 and 34 bit.
> 
> These three are all two bits more than some "regular" size --
> do those two extra bits have some special meaning perhaps,
> like an address space identifier or something?
> 
> > The Freescale's silicons is only support 34 bit address now.
> > Do you mean I should not use words -- 'should be <2>'?
> > The #address-cells should be assigned according the address mode
> > supported by silicon.
> 
> No.  The #address-cells is determined by the bus binding,
> so that all RapidIO busses on the planet can be represented
> in a similar way in the OF device tree.  Take for example
> the PCI binding, which gives you three address cells -- one
> to distinguish between different address spaces (configuration
> space, legacy I/O space, memory mapped space) and to contain
> some flags (prefetchable vs. non-prefetchable, etc.); the
> other two 32-bit cells contain a 64-bit address, although
> config and legacy I/O never are more than 32 bit, and many
> PCI devices can't do 64-bit addressing at all.
> 
> Now, there is no OF binding for RapidIO yet of course, but
> it would be good to start thinking about one while doing
> the binding for your specific controller -- it will make
> life easier down the line for everyone, including yourself.
> 
How about I add more words here for more clear expression?
Such as "<2> for 34 and 50 bit address, <3> for 66 bit address".

Thanks!
Wei.
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