linux-kernel - Re: [RFC v2 4/9] VFIO: platform: handler tests whether the IRQ is forwarded

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Date:	Thu, 11 Sep 2014 05:10:00 +0200
From:	Christoffer Dall <christoffer.dall@...aro.org>
To:	Eric Auger <eric.auger@...aro.org>
Cc:	eric.auger@...com, marc.zyngier@....com,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
	kvm@...r.kernel.org, alex.williamson@...hat.com,
	joel.schopp@....com, kim.phillips@...escale.com, paulus@...ba.org,
	gleb@...nel.org, pbonzini@...hat.com, linux-kernel@...r.kernel.org,
	patches@...aro.org, will.deacon@....com,
	a.motakis@...tualopensystems.com, a.rigo@...tualopensystems.com,
	john.liuli@...wei.com
Subject: Re: [RFC v2 4/9] VFIO: platform: handler tests whether the IRQ is
 forwarded

On Mon, Sep 01, 2014 at 02:52:43PM +0200, Eric Auger wrote:
> In case the IRQ is forwarded, the VFIO platform IRQ handler does not
> need to disable the IRQ anymore. In that mode, when the handler completes

add a comma after completes

> the IRQ is not deactivated but only its priority is lowered.
> 
> Some other actor (typically a guest) is supposed to deactivate the IRQ,
> allowing at that time a new physical IRQ to hit.
> 
> In virtualization use case, the physical IRQ is automatically completed
> by the interrupt controller when the guest completes the corresponding
> virtual IRQ.
> 
> Signed-off-by: Eric Auger <eric.auger@...aro.org>
> ---
>  drivers/vfio/platform/vfio_platform_irq.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/platform/vfio_platform_irq.c b/drivers/vfio/platform/vfio_platform_irq.c
> index 6768508..1f851b2 100644
> --- a/drivers/vfio/platform/vfio_platform_irq.c
> +++ b/drivers/vfio/platform/vfio_platform_irq.c
> @@ -88,13 +88,18 @@ static irqreturn_t vfio_irq_handler(int irq, void *dev_id)
>  	struct vfio_platform_irq *irq_ctx = dev_id;
>  	unsigned long flags;
>  	int ret = IRQ_NONE;
> +	struct irq_data *d;
> +	bool is_forwarded;
>  
>  	spin_lock_irqsave(&irq_ctx->lock, flags);
>  
>  	if (!irq_ctx->masked) {
>  		ret = IRQ_HANDLED;
> +		d = irq_get_irq_data(irq_ctx->hwirq);
> +		is_forwarded = irqd_irq_forwarded(d);
>  
> -		if (irq_ctx->flags & VFIO_IRQ_INFO_AUTOMASKED) {
> +		if (irq_ctx->flags & VFIO_IRQ_INFO_AUTOMASKED &&
> +						!is_forwarded) {
>  			disable_irq_nosync(irq_ctx->hwirq);
>  			irq_ctx->masked = true;
>  		}
> -- 
> 1.9.1
> 
It makes sense that these needs to be all controlled in the kernel, but
I'm wondering if it would be cleaner / more correct to clear the
AUTOMASKED flag when the IRQ is forwarded and have vfio refuse setting
this flag as long as the irq is forwarded?

-Christoffer
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