Re: Introducing a nanoMIPS port for Linux

From: Arnd Bergmann
Date: Thu May 03 2018 - 18:40:15 EST

On Wed, May 2, 2018 at 5:51 PM, James Hogan <jhogan@xxxxxxxxxx> 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. 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.