From: Catalin Marinas <catalin.marinas@arm.com>
To: Joakim Tjernlund <Joakim.Tjernlund@infinera.com>
Cc: "linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: Running/building an 32 bits kernel on A53 CPU?
Date: Tue, 2 Nov 2021 15:44:22 +0000 [thread overview]
Message-ID: <YYFc1g9F3DOvfCNs@arm.com> (raw)
In-Reply-To: <bce16a606400f4e24cb93350c7e419f69a579b07.camel@infinera.com>
On Tue, Nov 02, 2021 at 01:20:22PM +0000, Joakim Tjernlund wrote:
> On Fri, 2021-10-29 at 10:32 +0000, Joakim Tjernlund wrote:
> > On Fri, 2021-10-29 at 11:09 +0100, Catalin Marinas wrote:
> > > On Fri, Oct 29, 2021 at 08:27:35AM +0000, Joakim Tjernlund wrote:
> > > > In order to reduce RAM usage we are wondering if running an 32 bits
> > > > kernel on ARM A53 CPU is a good idea?
> > >
> > > No. Really.
> > >
> > > What's the RAM size on your SoC?
> >
> > 32MB + 4MB SRAM
> >
> > >
> > > > Is it possible to build such a kernel? If so, how to go about it?
> > > > Should one use ARCH=arm and a 32 bits toolchain or
> > > > ARCH=arm64 and 64 bits toolchain and adding 32 bits compile options?
> > >
> > > If you want a 32-bit kernel, you'd have to use ARCH=arm and a 32-bit
> > > toolchain. This would give you an ARMv7 kernel that can run on ARMv8
> > > hardware. But you'd miss errata workarounds for example and any other
> > > features that come with ARMv8.
>
> Anything else you can think of why 32 bits kernel is a bad idea?
32-bit kernels on arm64 hardware are not "officially" supported by the
maintainers (though there are some commercial deployments).
Given the amount of RAM, you might as well give 32-bit uClinux a try ;)
(even less tested).
> I do wonder why 64 bits A53 enforces SMP? I only have one core in my
> HW(custom ASIC)
We removed it because we were not aware of any such UP system. Note that
even with CONFIG_SMP enabled, the kernel still runs fine on a UP system.
I guess you want to get rid of extra code in the final image.
--
Catalin
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prev parent reply other threads:[~2021-11-02 15:45 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-29 8:27 Running/building an 32 bits kernel on A53 CPU? Joakim Tjernlund
2021-10-29 10:09 ` Catalin Marinas
2021-10-29 10:32 ` Joakim Tjernlund
2021-10-29 13:00 ` Robin Murphy
2021-10-29 13:36 ` Joakim Tjernlund
2021-11-02 13:20 ` Joakim Tjernlund
2021-11-02 15:44 ` Catalin Marinas [this message]
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