Re: [Qemu-devel] [PATCH for-1.6] mips_malta: do not raise exceptions when accessing invalid memory

["Andreas Färber" <afaerber@suse.de>]

Am 13.08.2013 12:05, schrieb James Hogan:
> On 12 August 2013 20:44, Aurelien Jarno <aurelien@aurel32.net> wrote:
>> Since commit c658b94f6e8c206c59d02aa6fbac285b86b53d2c, MIPS raises
>> exceptions when accessing invalid memory. This is not the correct
>> behaviour for MIPS Malta Core LV, as the GT-64120A system controller
>> just ignore undecoded access. This feature is used by the Linux kernel
>> to probe for some devices.
>>
>> Emulate the correct behaviour in QEMU by adding an empty slot covering
>> the entire memory space decoded by the GT-64120A.
>>
>> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
>> ---
> 
> <snip>
> 
>> @@ -908,6 +909,11 @@ void mips_malta_init(QEMUMachineInitArgs *args)
>>      DeviceState *dev = qdev_create(NULL, TYPE_MIPS_MALTA);
>>      MaltaState *s = MIPS_MALTA(dev);
>>
>> +    /* The whole address space decoded by the GT-64120A doesn't generate
>> +       exception when accessing invalid memory. Create an empty slot to
>> +       emulate this feature. */
>> +    empty_slot_init(0, 0x1fffffff);
> 
> Out of interest, any particular reason not to put this in
> hw/mips/gt64xxx_pci.c? As far as I can tell from your description it's
> specific to the GT-64* system controller rather than the malta board?

I was assuming that we didn't properly model that device when putting it
on the board directly, but if there is one then putting it into such a
device will avoid having to copy it into multiple boards.

Perhaps in that case we can even have a proper MemoryRegion in the
SysBus device instead of a separate empty slot pseudo-device?

FWIW gt64xxx_pci.c could certainly use some more love to eliminate
gt64120_register() and to create PCIDevice and PCIBus in the bridge
itself for instance...

Regards,
Andreas

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