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Date:   Fri, 16 Aug 2019 16:58:33 +0100
From:   Russell King - ARM Linux admin <linux@armlinux.org.uk>
To:     Aaro Koskinen <aaro.koskinen@iki.fi>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Martin Michlmayr <tbm@cyrius.com>,
        Peter Teichmann <lists@peter-teichmann.de>,
        Arnd Bergmann <arnd@arndb.de>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        soc@kernel.org, Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        Vinod Koul <vkoul@kernel.org>,
        linux-i2c <linux-i2c@vger.kernel.org>, dmaengine@vger.kernel.org,
        Dan Williams <dan.j.williams@intel.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 1/7] [RFC] ARM: remove Intel iop33x and iop13xx support
Message-ID: <20190816155833.GL13294@shell.armlinux.org.uk>
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On Fri, Aug 16, 2019 at 06:42:49PM +0300, Aaro Koskinen wrote:
> Hi,
> 
> On Wed, Aug 14, 2019 at 10:36:01AM +0200, Linus Walleij wrote:
> > On Mon, Aug 12, 2019 at 11:45 AM Martin Michlmayr <tbm@cyrius.com> wrote:
> > > As Arnd points out, Debian used to have support for various iop32x
> > > devices.  While Debian hasn't supported iop32x in a number of years,
> > > these devices are still usable and in use (RMK being a prime example).
> > 
> > I suppose it could be a good idea to add support for iop32x to
> > OpenWrt and/or OpenEmbedded, both of which support some
> > pretty constrained systems.
> 
> This platform is not really too constrained... E.g. on N2100 you have
> 512 MB RAM, SATA disks and gigabit ethernet. Not that different from
> mvebu that Debian currently (?) supports. Maybe with multiplatform they
> could support iop32x again.

Probably not.  The kernel has a dividing line between ARMv5 and ARMv6
where it's not possible to multiplatform across that boundary, so
you're already needing separate kernel images there.

Secondly, armhf distros won't be compatible with ARMv5, and to make
them compatible will make performance on armhf suffer - you have to
stop using barriers, exclusive load/store and a few other things.
You have to rely on the kuser page exported by the kernel (which is
now optional as it's deemed to be a security issue for ROP attacks)
for some things that such a userspace requires - such as NPTL support.

Effectively, ARMv5 is an entirely separate userspace distro from armhf.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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