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Date: Thu, 18 Jul 2013 18:24:11 +0100
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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To: Russell King - ARM Linux <linux@arm.linux.org.uk>
CC: Julien Grall <julien.grall@linaro.org>,
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        Arnd Bergmann <arnd@arndb.de>, Olof Johansson <olof@lixom.net>
Subject: Re: [PATCH] arm: choose debug/uncompress.h include when uncompress
 debug is disabledo
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On Thu, 18 Jul 2013, Russell King - ARM Linux wrote:
> On Thu, Jul 18, 2013 at 05:43:37PM +0100, Julien Grall wrote:
> > When Xen will boot, it will use one UART, given by the user, to be able
> > to log its information. Xen will not map the UART region and the IRQ to
> > dom0. Of course it will not be present in the device tree either. So if
> > Linux tries to access to this memory region, it will crash.
> > 
> > When Linux will boot as dom0, it will either use an hvc console or
> > another UART.
> > 
> > In case of multi-platform environments, there is no issue because when
> > CONFIG_DEBUG_UNCOMPRESS is disabled.
> > 
> > Now, in non-multiplatform environment, the decompressor will use a
> > pre-defined UART. This UART may be already used by Xen and Linux will
> > abort at the first access.
> > 
> > I think, the decompressor should be able to detect if the UART exists
> > (I'm not sure it's possible) or disabled at compile time uncompress log.
> > 
> > Do you have any better ideas?
> 
> Let me get this straight.
> 
> 1. You want to run an _existing_ platforms kernel under Xen, where the
>    platform assumes that it has various devices at various locations,
>    and will make direct accesses to those devices.
> 
> 2. You don't want to provide some of those devices, and you arrange for
>    those unprovided devices to fault.
> 
> Excuse me if I think that's really silly.

Unfortunately not all the platforms are available on multiplatform
kernels.
Also by the same argument, we wouldn't need device tree on
non-multiplatform kernels because we could hardcode almost anything.


> Lastly, aren't all ARMv7 kernels (therefore Xen supporting kernels)
> supposed to be part of the multiplatform kernel stuff now?

Most of them, yes. However some of them, like exynos5250, are not yet.