linux-kernel - Re: [RFC PATCH 4/9] irqchip: GIC: add support for forwarded interrupts

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Message-ID: <20140627131748.GT26276@arm.com>
Date:	Fri, 27 Jun 2014 14:17:48 +0100
From:	Will Deacon <will.deacon@....com>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"eric.auger@...aro.org" <eric.auger@...aro.org>,
	Christoffer Dall <christoffer.dall@...aro.org>
Subject: Re: [RFC PATCH 4/9] irqchip: GIC: add support for forwarded
 interrupts

Hi Marc,

On Wed, Jun 25, 2014 at 10:28:45AM +0100, Marc Zyngier wrote:
> Now that we've switched to EOImode == 1, prevent a forwarded interrupt
> from being deactivated after its priority has been dropped.
> 
> Also add support for the interrupt state to be saved/restored.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> ---
>  drivers/irqchip/irq-gic.c | 48 +++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 42 insertions(+), 6 deletions(-)

[...]

> +static void gic_irq_set_fwd_state(struct irq_data *d, u32 val, u32 mask)
> +{
> +	if (mask & IRQ_FWD_STATE_PENDING)
> +		gic_poke_irq(d, (val & IRQ_FWD_STATE_PENDING) ? GIC_DIST_ENABLE_SET : GIC_DIST_ENABLE_CLEAR);
> +	if (mask & IRQ_FWD_STATE_ACTIVE)
> +		gic_poke_irq(d, (val & IRQ_FWD_STATE_ACTIVE) ? GIC_DIST_ACTIVE_SET : GIC_DIST_ACTIVE_CLEAR);
> +	if (mask & IRQ_FWD_STATE_MASKED)
> +		gic_poke_irq(d, (val & IRQ_FWD_STATE_MASKED) ? GIC_DIST_ENABLE_CLEAR : GIC_DIST_ENABLE_SET);

Given that this isn't atomic and KVM only cares about ACTIVE, why not change
mask to be a single state only? Renumbering the states so that's not bits
would help to enforce this (i.e. make IRQ_FWD_STATE_ACTIVE 0, PENDING 1,
...).

That would also allow you to switch on the state and return early.

> +static u32 gic_irq_get_fwd_state(struct irq_data *d, u32 mask)
> +{
> +	u32 val = 0;
> +
> +	if (mask & IRQ_FWD_STATE_PENDING && gic_peek_irq(d, GIC_DIST_ENABLE_SET))
> +		val |= IRQ_FWD_STATE_PENDING;
> +	if (mask & IRQ_FWD_STATE_ACTIVE && gic_peek_irq(d, GIC_DIST_ACTIVE_SET))
> +		val |= IRQ_FWD_STATE_ACTIVE;
> +	if (mask & IRQ_FWD_STATE_MASKED && !gic_peek_irq(d, GIC_DIST_ENABLE_SET))
> +		val |= IRQ_FWD_STATE_MASKED;

*and* you could peek GIC_DIST_ENABLE_SET in one place here.

Will
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