Re: [Qemu-devel] [PATCH 2/2] vga: Fix portio list conversion fallouts

[Jan Kiszka <jan.kiszka@web.de>]

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On 2011-09-18 18:51, Avi Kivity wrote:
> On 09/18/2011 07:28 PM, Jan Kiszka wrote:
>> On 2011-09-18 17:51, Avi Kivity wrote:
>> >  On 09/18/2011 03:44 PM, Jan Kiszka wrote:
>> >>  From: Jan Kiszka<jan.kiszka@siemens.com>
>> >>
>> >>  Fix copy&paste errors and reduce duplications of the BOCHS VBE
>> ranges.
>> >>
>> >>  Signed-off-by: Jan Kiszka<jan.kiszka@siemens.com>
>> >>  ---
>> >>
>> >>    #ifdef CONFIG_BOCHS_VBE
>> >>    static const MemoryRegionPortio vbe_portio_list[] = {
>> >>  -# ifdef TARGET_I386
>> >>        { 0, 1, 2, .read = vbe_ioport_read_index, .write =
>> >>  vbe_ioport_write_index },
>> >>  +# ifdef TARGET_I386
>> >
>> >  Strange how the card knows what target it's plugged into.  Fixing this
>> >  is going to involve major pain - need to update the bios and need to
>> >  provide backwards compatibility.  All this assuming guests don't
>> >  hardcode the address.
>> >
>> >  Anyway I find the deduplication makes the code harder to read.
>>
>> That line is rather tricky to deduplicate in mind. So it's not nice for
>> our readers keeping it duplicated around.
> 
> I don't think it should be deduplicated.  The device is providing two
> separate ABIs.

Yes, two ABIs, and the only difference is the offset of the data register.

> 
>> >
>> >>        { 1, 1, 2, .read = vbe_ioport_read_data, .write =
>> >>  vbe_ioport_write_data },
>> >>    # else
>> >>  -    { 0, 2, 2, .read = vbe_ioport_read_index, .write =
>> >>  vbe_ioport_write_index },
>> >>  -    { 2, 2, 2, .read = vbe_ioport_read_data, .write =
>> >>  vbe_ioport_write_data },
>> >>  +    { 2, 1, 2, .read = vbe_ioport_read_data, .write =
>> >>  vbe_ioport_write_data },
>> >
>> >  Is this correct?  length 1 region with size 2?
>>
>> Yes, it prevents accesses on base+1.
>>
> 
> Why disallow it?

Did anyone check that something useful or at least valid comes out of
the handlers when doing this so far impossible access?

Jan


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