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Re: [U-Boot] MIPS UHI spec

To: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Subject: Re: [U-Boot] MIPS UHI spec
From: Andrew Bresticker <abrestic@chromium.org>
Date: Thu, 26 Feb 2015 10:23:45 -0800
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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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?  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

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