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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 18 Oct 2018 10:36:45 +0200
Message-ID: <CAK8P3a0wRPfXm3wupQd6RdN6L8CvjD0HX_Bk61VBxOYeNCh+FA@mail.gmail.com>
Subject: Re: [PATCH V9 00/21] C-SKY(csky) Linux Kernel Port
To:     Guo Ren <ren_guo@c-sky.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        David Miller <davem@davemloft.net>,
        gregkh <gregkh@linuxfoundation.org>,
        Christoph Hellwig <hch@infradead.org>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Rob Herring <robh@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        DTML <devicetree@vger.kernel.org>,
        Rob Herring <robh+dt@kernel.org>, c-sky_gcc_upstream@c-sky.com
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On Thu, Oct 18, 2018 at 6:11 AM Guo Ren <ren_guo@c-sky.com> wrote:
>
> On Wed, Oct 17, 2018 at 05:58:46PM +0200, Arnd Bergmann wrote:
> > On Tue, Oct 16, 2018 at 4:58 AM Guo Ren <ren_guo@c-sky.com> wrote:
> > >
> > > This is the 9th version patchset to add the Linux kernel port for
> > > C-SKY(csky) based on linux-4.19-rc3.
> > >
> > > There are only a few changes between V8 patchset. Hope it could be
> > > merged into linux-4.20 and I'm very grateful for any help.
> >
> > I've gone through the entire series once more and saw no show-stoppers.
> > The last patch looked like it introduced a bug, but with that one dropped,
> > I'm happy for the architecture to get merged, unless anyone else
> > has any last-minute concerns. (Alternatively, explain why I'm wrong
> > and the code works correctly, of course).
> Ok and thx for the job of csky subsystem.
>
> >
> > I'd appreciate having someone else take another look at the signal
> > handling code, the atomics, and the DT bindings and provide another
> > Ack for those.
> >
> > The remaining open question is about the 32-bit time_t interfaces.
> > With 4.20, I did not manage to get the required system calls in place
> > for using 64-bit time_t in a new architecture, so you will at least
> > start out using 32-bit time_t and likely have to keep supporting
> > that going forward, unless we decide to break the ABI here later
> > on .This is something we normally don't do, but we might make
> > an exception here, under the assumption that there are no
> > existing users with the ABI. We can debate that once we get there.
> We support uclibc-ng and glibc.
>
> 1. For uclibc-ng, linux-4.20 could run with it.
>
> 2. For glibc, Maybe we could support 32-bit + 64-bit time_t with
> KERNEL_VERSION, or just only 64-bit then linux-4.20 couldn't work with
> the csky first glibc release.

Yes, it is always an option to make glibc more restrictive than the kernel.
We could also just make it a configuration option in the kernel whether
the system calls are provided, so they don't use memory for the
implementation.

You will probably want musl support at some point. musl-1.x always
uses 32-bit time_t today, but musl-2.x will use the 64-bit interfaces,
so just waiting a bit will probably make it work out for you.

        Arnd