[U-Boot] MIPS UHI spec

[James Hogan]

On 26/02/15 12:37, Daniel Schwierzeck wrote:
> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton at imgtec.com>:
>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>> Hi Daniel,
>>>
>>> The spec for MIPS Unified Hosting Interface is available here:
>>>
>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>
>>> As we have previously discussed, this is an ideal place to
>>> define the handover of device tree data from bootloader to
>>> kernel. Using a0 == -2 and defining which register(s) you
>>> need for the actual data will fit nicely. I'll happily
>>> include whatever is decided into the next version of the spec.
> 
> this originates from an off-list discussion some months ago started by
> John Crispin.
> 
> (CC +John, Ralf, Jonas, linux-mips)
> 
>>
>> (CC +Andrew, Ezequiel, James, James)
>>
>> On the talk of DT handover, this recent patchset adding support for a
>> system doing so to Linux is relevant:
>>
>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>
>> I'm also working on a system for which I'll need to implement DT
>> handover very soon. It would be very nice if we could agree on some
>> standard way of doing so (and eventually if the code on the Linux side
>> can be generic enough to allow a multiplatform kernel).
>>
> 
> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
> blob. It is a simple extension and should not interfere with the
> various legacy boot interfaces.

I was just looking at Andrew's patch:
http://patchwork.linux-mips.org/patch/9549/

How would the other registers (i.e. $a2 and $a3) be defined for this
boot interface? I'm guessing any future extensions are envisioned to use
a different negative value of $a0, in which case treating them as
unused/undefined is fine, but perhaps that should be spelt out in the
UHI spec?

Cheers
James

> 
> U-Boot mainline code is almost ready for DT handover. I have prepared
> a patch [1] which completes it by implementing my proposal.
> 
> [1] http://git.denx.de/?p=u-boot/u-boot-mips.git;a=commitdiff;h=3464e8de491c640d14d72853a741cc367ebabc79
> 

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