Re: [Qemu-devel] ISA BIOS mapping for system flash emulation

[Jan Kiszka]

On 2012-11-01 17:13, Jordan Justen wrote:
> On Wed, Oct 31, 2012 at 11:57 PM, Jan Kiszka <address@hidden> wrote:
>> On 2012-11-01 03:55, Jordan Justen wrote:
>>> On Tue, Oct 30, 2012 at 11:14 PM, Jan Kiszka <address@hidden> wrote:
>>>> Hi Jordan,
>>>>
>>>> I was starring at pc_isa_bios_init and wondering why you are creating a
>>>> copy of the system flash for the low ISA range instead of using an alias
>>>> here as well, just like old_pc_system_rom_init does. That means the ISA
>>>> BIOS range can run out of sync when the system flash is updated during
>>>> runtime and requires a restart of QEMU then. Switching to an alias would
>>>> also allow some code consolidation. Can you explain the idea behind the
>>>> current version?
>>>
>>> I'm pretty sure I tried this and found that it did not work on the flash 
>>> device.
>>>
>>> I wrote an email to the list on Oct 17, 2011 about this, but I didn't
>>> get a response. (Re: [Qemu-devel] [PATCH 2/4] pc: Support system flash
>>> memory with pflash)
>>
>> Can you be more specific how/when it failed? A trivial test cannot
>> confirm this so far.
> 
> I reproduced this on 1b89fafe (where x86-flash was introduced). When I
> setup the alias, I saw random data in the F000 segment.
> 
> When I tried the same thing on the current master (patch attached), it
> appeared to work correctly.

I vaguely remember issues with aliasing in the early memory region days,
maybe that was causing it. As there is no conceptual reason to avoid an
alias, let's file a refactoring patch.

Jan

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