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Re: [U-Boot] MIPS UHI spec

To: Andrew Bresticker <abrestic@chromium.org>
Subject: Re: [U-Boot] MIPS UHI spec
From: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Date: Fri, 27 Feb 2015 11:44:45 +0100
Cc: Paul Burton <paul.burton@imgtec.com>, Matthew Fortune <Matthew.Fortune@imgtec.com>, "u-boot@lists.denx.de" <u-boot@lists.denx.de>, Ezequiel Garcia <ezequiel.garcia@imgtec.com>, James Hartley <james.hartley@imgtec.com>, James Hogan <james.hogan@imgtec.com>, John Crispin <blogic@openwrt.org>, Jonas Gorski <jogo@openwrt.org>, Ralf Baechle <ralf@linux-mips.org>, Linux-MIPS <linux-mips@linux-mips.org>, cernekee@chromium.org
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2015-02-26 19:23 GMT+01:00 Andrew Bresticker <abrestic@chromium.org>:
> Hi,
>
> On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
> <daniel.schwierzeck@gmail.com> wrote:
>> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@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).
>
> +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?

no, but with its publication the MIPS UHI spec is kind of official.
AFAIK patches to support UHI in gcc, gdb, U-Boot etc. are already
submitted or prepared. Matthew suggested that new boot protocols
should be compliant with UHI. I think the ARM convention does not fit
to UHI.

> It's still early
> enough that we could change the DT handover for Pistachio, but it
> would be good to agree on something soon.
>
> Thanks,
> Andrew

-- 
- Daniel

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