Re: [Qemu-devel] [PATCH v2 07/11] versatile_pci: Implement the correct PCI IRQ mapping

[Peter Maydell]

On 28 March 2013 10:28, Peter Maydell <address@hidden> wrote:
> On 26 March 2013 21:12, Michael S. Tsirkin <address@hidden> wrote:
>> On Tue, Mar 26, 2013 at 11:17:55AM +0000, Peter Maydell wrote:
>>> I'm happy to provide some other way for QEMU to detect a
>>> new working kernel if you want to implement one in the
>>> kernel, if that's cleaner.
>>
>> That's why I suggested writing some number at offset 0x08
>> (that's revision ID) in configuration space of device 0 on bus 0.
>> It's guaranteed harmless on real hardware and QEMU could detect this
>> write and say "aha new kernel, even though it uses #27".
>
> OK, that makes sense.

In fact I've just realised that "allow new kernels to use #27
without getting the back-compat broken irq mapping" conflicts
with "allow new kernels to kexec old broken kernels". So the
easiest approach is just to drop the code which allows us to
switch back to broken mode again. Then the new kernel's init
code can force non-broken mode by writing something other than
#27 to some device's PCI_INTERRUPT_LINE register, and then
is free to use #27 if it wants to.

-- PMM