Re: [RFC PATCH] kvmtool: remove 8250 IRQ line reset on device_init

[Andre Przywara <andre.przywara@arm.com>]

On 12/01/15 17:41, Will Deacon wrote:
> On Fri, Jan 09, 2015 at 03:58:19PM +0000, Andre Przywara wrote:
>> Currently we reset the KVM interrupt line on initializing the 8250
>> serial device emulation.
>> For ARM this creates a problem where we use the in-kernel IRQ chip
>> before having fully initialized it. But with the new kernel interface
>> we cannot finish the GIC initialization before we know the number of
>> used IRQs, so we have to wait until all devices have been created and
>> initialized.
>> Since the in-kernel GIC emulation resets the IRQ line anyway and also
>> QEMU gets away without resetting it, the easiest solution is to drop
>> the IRQ line reset.
>>
>> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>> ---
>> Hi Pekka,
>>
>> this patch is an easy fix for our problems with Marc's kvmtool tree
>> and 3.19-rc (setting number of IRQs after the GIC has been used
>> already). I see that this basically reverts:
>>
>>> commit 2ca9e37193ca5f5df5726e0061dc749829295435
>>> Author: Pekka Enberg <penberg@kernel.org>
>>> Date:   Sun Jan 23 11:49:39 2011 +0200
>>>
>>>     kvm,8250: Fix device initial state
>>>     
>>>     This patch fixes 8250 device initial state for registers and IRQ based
>>>     on what Qemu does.
>>
>> Do you (or does anyone) know of the issue that this patch fixed?
>> This is four years old and from what I see QEMU does no longer the
>> mentioned IRQ reset(?).
>> Reworking kvmtool to avoid this issue sound rather painful.
> 
> I'm fine with this from an ARM point-of-view.
> 
>   Acked-by: Will Deacon <will.deacon@arm.com>
> 
> Have you tested this on x86?

Yes, that worked as well. Booting into an initrd, flooding the console
with output: no issues.

Cheers,
Andre.

> 
>>  tools/kvm/hw/serial.c |    1 -
>>  1 file changed, 1 deletion(-)
>>
>> diff --git a/tools/kvm/hw/serial.c b/tools/kvm/hw/serial.c
>> index 270e6182..2f19ba8 100644
>> --- a/tools/kvm/hw/serial.c
>> +++ b/tools/kvm/hw/serial.c
>> @@ -406,7 +406,6 @@ static int serial8250__device_init(struct kvm *kvm, struct serial8250_device *de
>>  
>>  	ioport__map_irq(&dev->irq);
>>  	r = ioport__register(kvm, dev->iobase, &serial8250_ops, 8, dev);
>> -	kvm__irq_line(kvm, dev->irq, 0);
>>  
>>  	return r;
>>  }
>> -- 
>> 1.7.9.5
>>
>