linux-kernel - Re: Introducing a nanoMIPS port for Linux

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Date:   Fri, 4 May 2018 14:24:33 +0100
From:   James Hogan <jhogan@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Ralf Baechle <ralf@...ux-mips.org>,
        "open list:RALINK MIPS ARCHITECTURE" <linux-mips@...ux-mips.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Paul Burton <paul.burton@...s.com>,
        Matt Redfearn <matt.redfearn@...s.com>,
        Marcin Nowakowski <marcin.nowakowski@...s.com>,
        Matthew Fortune <Matthew.Fortune@...s.com>
Subject: Re: Introducing a nanoMIPS port for Linux

On Thu, May 03, 2018 at 06:40:07PM -0400, Arnd Bergmann wrote:
> On Wed, May 2, 2018 at 5:51 PM, James Hogan <jhogan@...nel.org> wrote:
> 
> > Due to the binary incompatibility between previous MIPS architecture
> > generations and nanoMIPS, and the significantly revamped compiler ABI,
> > where for the first time, a single Linux kernel would not be expected to
> > handle both old and new ABIs, we have decided to also take the
> > opportunity to modernise the Linux user ABI for nanoMIPS, making as much
> > use of generic interfaces as possible and modernising the true
> > architecture specific parts.
> >
> > This is similar to what a whole new kernel architecture would be
> > expected to adopt, but has been done within the existing MIPS
> > architecture port to allow reuse of the existing MIPS code, most of
> > which does not depend on these ABI specifics. Details of the proposed
> > Linux user ABI changes for nanoMIPS can be found here:
> 
> While I haven't looked at the individual changes, I wonder whether
> it would be useful to make this new ABI use 64-bit time_t from
> the start, using the new system calls that Deepa and I have been
> posting recently.

Personally I'm all for squeezing as much API cleanup in as possible
before its merged, though obviously there'll be a point when the ABI may
need to be frozen, at which point we'll mostly have to accept what we
have within reason.

> There are still a few things to be worked out:
> only the first of four sets of syscall patches is merged so far,
> and we have a couple of areas that will require further ABI changes
> (sound, sockets, media and maybe a couple of smaller drivers),
> so it depends on the overall timing. If you would otherwise merge
> the patches quickly, then it may be better to just follow the existing
> 32-bit architectures and add the 64-bit entry points when we do it
> for everyone.

I think it'll likely be a couple of cycles before it gets merged anyway.
There's still work to do, and limited resources.

Cheers
James

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