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Re: [U-Boot] MIPS UHI spec

To: Daniel Schwierzeck <>
Subject: Re: [U-Boot] MIPS UHI spec
From: Andrew Bresticker <>
Date: Thu, 26 Feb 2015 10:23:45 -0800
Cc: Paul Burton <>, Matthew Fortune <>, "" <>, Ezequiel Garcia <>, James Hartley <>, James Hogan <>, John Crispin <>, Jonas Gorski <>, Ralf Baechle <>, Linux-MIPS <>,
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On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
<> wrote:
> 2015-02-26 11:17 GMT+01:00 Paul Burton <>:
>> 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:
>>> 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:
>> 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).

+1.  I would like to see this happen as well.

> 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.
> U-Boot mainline code is almost ready for DT handover. I have prepared
> a patch [1] which completes it by implementing my proposal.

Hmm... we decided to follow the ARM convention here ($a0 = 0, $a1 =
-1, $a2 = physical address of DTB), which is also what the BMIPS
platform (submitted by Kevin) is using for DT handover.  Is there
already a platform using the protocol you described?  It's still early
enough that we could change the DT handover for Pistachio, but it
would be good to agree on something soon.


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