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Re: [Xen-devel] Re: [XenPPC] [PATCH] [POWERPC] fix vga.c compilation

To: Alex Williamson <alex.williamson@xxxxxx>
Subject: Re: [Xen-devel] Re: [XenPPC] [PATCH] [POWERPC] fix vga.c compilation
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Wed, 16 Aug 2006 15:24:38 +0100
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On 16/8/06 2:59 pm, "Alex Williamson" <alex.williamson@xxxxxx> wrote:

>    In general this looks a lot better, but I think ia64 is still going
> to have trouble with the chunk below.  It seems that a VGA card
> operating in a standard text mode doesn't necessarily respond to all of
> these addresses.  On some ia64 platforms that causes a hard fail
> response (the bus goes fatal and a reboot follows).  On my system, the
> 0xB8000 test looks like it will probably work, but we never get there
> because either the 0xA0000 or the 0xB0000 test will cause the hardfail.
> Do we need to poke the card through I/O port space to get it into the
> right mode before probing it in MMIO space?  I don't know enough about
> the VGA programming model to be able to do that.  The card works once we
> start talking to it correctly, but this probe is a little too brute
> force.  Thanks,

Actually I'm not sure this is particularly necessary for headless x86
either. I could move the test to the end of setup_vga(), and only probe
0xb8000? x86 is more 'resilient' to random memory and port accesses. I don't
think it'll matter that we do lots of port accesses even if a vga adapter
isn't present. If we keep the conventional-ram test as well, then that'll be
the same level of checking that Linux does on ia64.

 -- Keir

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