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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: Fri, 27 Feb 2015 09:28:44 -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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On Fri, Feb 27, 2015 at 2:44 AM, Daniel Schwierzeck
<daniel.schwierzeck@gmail.com> wrote:
> 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.

Ok, I think we can change the boot protocol on Pistachio to match UHI then.

-Andrew

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