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Re: [Qemu-ppc] [Qemu-devel] [PATCH v3 06/14] sam460ex: Don't size flash

From: Markus Armbruster
Subject: Re: [Qemu-ppc] [Qemu-devel] [PATCH v3 06/14] sam460ex: Don't size flash memory to match backing image
Date: Fri, 08 Mar 2019 15:27:05 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)

Philippe Mathieu-Daudé <address@hidden> writes:

> On 3/7/19 2:03 PM, Markus Armbruster wrote:
>> Machine "sam460ex" maps its flash memory at address 0xFFF00000.  When
>> no image is supplied, its size is 1MiB (0x100000), and 512KiB of ROM
>> get mapped on top of its second half.  Else, it's the size of the
>> image rounded up to the next multiple of 64KiB.
>> The rounding is actually useless: pflash_cfi01_realize() fails with
>> "failed to read the initial flash content" unless it's a no-op.
>> I have no idea what happens when the pflash's size exceeds 1MiB.
>> Useful outcomes seem unlikely.
> You now have! [*] "Hardwiring address lines leaves part of the hardware
> unaddressable." Anything bigger than 1MiB mapped at 0xFFF00000 only has
> the first MiB addressable. IOW anything above 1MiB is unaddressable, but
> you still can map a such bigger flash.
> [*] https://lists.gnu.org/archive/html/qemu-devel/2019-03/msg01380.html

Well, that's what would happen with real hardware.  But this device
model doesn't actually model address lines.  It simply asks
pflash_cfi01_register() to map blk_getlength() bytes at the base
address.  If you ask it to map gigabytes, it'll happily do so (as long
as malloc plays along).

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