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
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YYFc1g9F3DOvfCNs@arm.com \
--to=catalin.marinas@arm.com \
--cc=Joakim.Tjernlund@infinera.com \
--cc=linux-arm-kernel@lists.infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.