[lowrisc-dev] Re: [sw-dev] Is a de facto standard memory map helpful or harmful?

Arnd Bergmann arnd at arndb.de
Thu Jul 14 14:01:29 BST 2016


On Thursday, July 14, 2016 5:44:20 AM CEST krste at berkeley.edu wrote:
> >>>>> On Wed, 13 Jul 2016 20:21:22 +0200, Karsten Merker <merker at debian.org> said:
> | Hello,
> 
> | is there some documentation available regarding this "RISC-V
> | configuration string"?  Alex' comment sounds like it is intended
> | as an alternative to device-tree, in which case I wonder a bit
> | whether adding yet-another-hardware-description-format instead of
> | using device-tree makes sense respectively which are the
> | advantages of a new hardware description format compared to
> | device-tree.
> 
> It's documented in a chapter in the 1.9 draft.  It is certainly open
> for discussion.  We discuss this reasons for not using device tree in
> commentary in chapter.  In short, we wanted to avoid a binary
> encoding, particularly one that is a poor fit for standard RISC-V Unix
> machines (little endian and > 32 bits.
> 
> We couldn't see any advantage to adding another layer of cruft of top
> of a poorly thought out standard.
> 
> Our config string is a simple plain printable UTF-8 string, and we've
> already provided a library for managing this in the Linux port.  We
> will relicense this code under BSD.

I think such code is unlikely to get merged into the Linux kernel
though, there will be significant resistance for subsystem maintainers
in adding yet another boot loader interface.

However, you could have your own interface for the first-stage bootloader,
and then load something like the pxa-impedence-matcher[1] that converts
the data into normal DTB format before starting the kernel.

	Arnd

[1] https://github.com/zonque/pxa-impedance-matcher



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