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

[Will Deacon <will.deacon@arm.com>]

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?

Will


>  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
>