linux-kernel - Re: [RFC PATCH 3/9] irqchip: GIC: Convert to EOImode == 1

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Message-ID: <20140806113054.GB14205@cbox>
Date:	Wed, 6 Aug 2014 13:30:54 +0200
From:	Christoffer Dall <christoffer.dall@...aro.org>
To:	Peter Maydell <peter.maydell@...aro.org>
Cc:	Marc Zyngier <marc.zyngier@....com>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	arm-mail-list <linux-arm-kernel@...ts.infradead.org>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will.deacon@....com>,
	Eric Auger <eric.auger@...aro.org>
Subject: Re: [RFC PATCH 3/9] irqchip: GIC: Convert to EOImode == 1

On Wed, Jun 25, 2014 at 03:06:33PM +0100, Peter Maydell wrote:
> On 25 June 2014 10:28, Marc Zyngier <marc.zyngier@....com> wrote:
> > For this case, the GIC architecture provides EOImode == 1, where:
> > - A write to the EOI register drops the priority of the interrupt and leaves
> > it active. Other interrupts at the same priority level can now be taken,
> > but the active interrupt cannot be taken again
> > - A write to the DIR marks the interrupt as inactive, meaning it can
> > now be taken again.
> >
> > We only enable this feature when booted in HYP mode. Also, as most device
> > trees are broken (they report the CPU interface size to be 4kB, while
> > the GICv2 CPU interface size is 8kB), output a warning if we're booted
> > in HYP mode, and disable the feature.
> 
> Does that mean you guarantee not to write to the DEACTIVATE
> register if not booted in Hyp mode? I ask because QEMU's
> GIC emulation doesn't emulate that register, so it would be
> useful to know if this patch means newer kernels are going to fall
> over under TCG QEMU...
> 
> (The correct fix, obviously, is to actually implement the QEMU
> support for split prio-drop and deactivate. Christoffer, you're our
> GIC emulation expert now, right? :-) )
> 
Missed this.  Sure, I can have a go at that some time, there are a
number of things I've been meaning to look at in the QEMU GIC emulation
code.

-Christoffer
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