Re: Single MIPS kernel

[Joshua Kinard <kumba@gentoo.org>]

On 10/22/2014 21:02, Ben Hutchings wrote:
> On Thu, 2014-10-23 at 01:22 +0200, Ralf Baechle wrote:
>> On Wed, Oct 22, 2014 at 11:15:40PM +0100, Ben Hutchings wrote:
>>
>>>>
>>>> That's probably more of an implementation detail.  I'm more concerned about
>>>> the overall bloat.  I think many embedded users are so addivted to benchmark
>>>> results that this going to make or break the whole scheme.
>>>
>>> If you can make relocation a configuration option (as on x86), it would
>>> allow distributions to build multiplatform kernels without preventing
>>> embedded users from building a kernel optimised for their specific
>>> system.  But I know very little about MIPS or how intrusive the changes
>>> for relocation would have to be.  Perhaps it would be too much of a
>>> maintenance burden to make this an option.
>>
>> The scope of the changes is relativly limited - we're much more concerned
>> about the impact on binary size, memory size or performance of the
>> various approaches under discussion.
>>
>> I wonder kernels for which platforms would Debian want to unify?
> 
> I don't have high expectations for being able to unify those we
> currently support.  Realistically, I expect that most development effort
> will go into new platforms.  (What we saw with ARM was that
> multi-platform was implemented for most ARMv7 platforms (for which we
> now need only 2 configurations) but only slowly for older chips (4
> configurations, and that's after dropping 2 platforms).)
> 
> Anyway, we have one 32-bit configuration for each byte order
> (4kc-malta), and the following 64-bit configurations:
> 
> [big-endian]
> r4k-ip22:      CONFIG_SGI_IP22, CONFIG_CPU_R4X00
> r5k-ip32:      CONFIG_SGI_IP32, CONFIG_CPU_R5000

As far as I know, IRIX includes kernels specific to each SGI system (IPxx), but
it seems they're CPU agnostic.  They are relocatable, though.  Been awhile
since I watched sash boot followed by an IRIX kernel, but it does 3-4
relocations before finally booting.  So a relocatable MIPS kernel on the SGI
platforms seems possible.  Probably requires arcane knowledge of ARCS, though.

Bootloader-wise, Stan's 'arcload' can handle booting multiple kernels across
various SGI platforms.  We used it on the Gentoo SGI LiveCD back in 2006 to
create a single CD that could boot on IP22, IP27, IP30, & IP32, using different
kernels for each system and CPU (I think there was one volume header slot left
at the end for arcload itself).

-- 
Joshua Kinard
Gentoo/MIPS
kumba@gentoo.org
4096R/D25D95E3 2011-03-28

"The past tempts us, the present confuses us, the future frightens us.  And our
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--Emperor Turhan, Centauri Republic