linux-kernel - Re: [PATCH 1/2] armv8: aarch32: Execute 32-bit Linux for LayerScape platforms

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Message-ID: <2017806.nj5EEu7nrO@wuerfel>
Date:   Fri, 23 Sep 2016 16:44:25 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     Robin Murphy <robin.murphy@....com>,
        Stuart Yoder <stuart.yoder@....com>,
        Alison Wang <b18965@...escale.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Fabio Estevam Estevam <fabio.estevam@....com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Scott Wood <scott.wood@....com>, Leo Li <leoyang.li@....com>,
        Jason Jin <jason.jin@....com>
Subject: Re: [PATCH 1/2] armv8: aarch32: Execute 32-bit Linux for LayerScape platforms

On Friday, September 23, 2016 3:24:12 PM CEST Robin Murphy wrote:
> On 23/09/16 15:01, Stuart Yoder wrote:
> Otherwise you can
> always simply run your own shim at EL2 to drive an AArch32 EL1 (it'll
> need to trap and translate subsequent SMC calls for e.g. PSCI).
> 
> > If there is such a requirement, it's something begging for standardization.
> > Doesn't make sense for multiple divergent approaches for switching from
> > aarch64/EL2 to aarch32/EL2.
> 
> Perhaps - I did briefly look into how hard it would be to write a proper
> SMC service handler to do this (since ATF does have a framework for such
> things), but concluded it would be more than 10 minutes' work and just
> cheated instead. It's certainly something which could be raised with the
> firmware folks.

If we end up allowing all arm64 platforms to be enabled in arch/arm,
we could perhaps create a generic implementation that does both of
those things, i.e.

- Take the arm32 kernel Image or zImage file, wrap it inside of a binary
  that implements the arm64 boot protocol.
- When that starts up, try to use the new PSCI call to jump into
  the arm32 kernel
- If PSCI failed and we are running in EL2, implement the shim
  and start the arm32 kernel in EL1 mode

	Arnd