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Re: [RFC PATCH-for-5.1? v3 2/2] hw/isa/isa-bus: Ensure ISA I/O regions a


From: Philippe Mathieu-Daudé
Subject: Re: [RFC PATCH-for-5.1? v3 2/2] hw/isa/isa-bus: Ensure ISA I/O regions are 8/16/32-bit accessible
Date: Tue, 21 Jul 2020 14:55:06 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0

On 7/21/20 2:41 PM, Peter Maydell wrote:
> On Tue, 21 Jul 2020 at 13:31, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>>
>> Since commit 5d971f9e67 we don't accept mismatching sizes
>> in memory_region_access_valid(). This gives troubles when
>> a device is on an ISA bus, because the CPU is free to use
>> 8/16-bit accesses on the bus (or up to 32-bit on EISA bus),
>> regardless what range is valid for the device.
>>
>> Monkey-patch the ISA device MemoryRegionOps to force it
>> to accepts 8/16/32-bit accesses. This should be reverted
>> after the release and fixed in a more elegant manner.
> 
> Do we need something similar for isa_register_portio_list(),
> or is that function OK ?
> 
> Do we have a view on what the 'more elegant manner' would look like?

What I suggested on IRC is a isabus->address_space_io is not assigned
by the bus creator but created internally as a MemoryRegion container
accepting 8/16 (ISA bus) or 8/16/32-bit (EISA bus) accesses from the I/O
address space, and this MR uses memory::access_with_adjusted_size()
(or similar) to access the registered portio devices.

We already have isa_address_space_io() to access
isabus->address_space_io.

isa_bus_new() could takes an 'is_eisa' boolean argument to select
between the adjusting MR.

> 
> thanks
> -- PMM
> 



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