linux-kernel - Re: [PATCH v4 16/24] xen: clear IRQ_NOAUTOEN and IRQ

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Date:	Fri, 14 Sep 2012 15:28:18 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Marc Zyngier <marc.zyngier@....com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"Tim (Xen.org)" <tim@....org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 16/24] xen: clear IRQ_NOAUTOEN and IRQ_NOREQUEST

On Fri, 14 Sep 2012, Marc Zyngier wrote:
> On 14/09/12 15:13, Stefano Stabellini wrote:
> > On Fri, 14 Sep 2012, Marc Zyngier wrote:
> >> On 14/09/12 12:13, Stefano Stabellini wrote:
> >>> Reset the IRQ_NOAUTOEN and IRQ_NOREQUEST flags that are enabled by
> >>> default on ARM. If IRQ_NOAUTOEN is set, __setup_irq doesn't call
> >>> irq_startup, that is responsible for calling irq_unmask at startup time.
> >>> As a result event channels remain masked.
> >>>
> >>> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> >>> Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> >>> ---
> >>>  drivers/xen/events.c |    1 +
> >>>  1 files changed, 1 insertions(+), 0 deletions(-)
> >>>
> >>> diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> >>> index 5ecb596..8ffb7b7 100644
> >>> --- a/drivers/xen/events.c
> >>> +++ b/drivers/xen/events.c
> >>> @@ -836,6 +836,7 @@ int bind_evtchn_to_irq(unsigned int evtchn)
> >>>  		struct irq_info *info = info_for_irq(irq);
> >>>  		WARN_ON(info == NULL || info->type != IRQT_EVTCHN);
> >>>  	}
> >>> +	irq_clear_status_flags(irq, IRQ_NOREQUEST|IRQ_NOAUTOEN);
> >>
> >> This one just sent a shiver down my spine. Are you doing this for a PPI?
> > 
> > Not really: even though there is just one source of event notifications
> > (that is a PPI), we have many event channels. When a domain receives a
> > notification (via the PPI), it checks on a bitmask to which event channel
> > it corresponds. From the Linux point of view every event channel is a
> > Linux irq belonging to the xen_dynamic_chip (see
> > drivers/xen/events.c:xen_dynamic_chip).
> > 
> > So here I am not doing this for the one PPI, but I am doing this for
> > every Linux irq (of chip xen_dynamic_chip) that represents an event
> > channel.
> 
> So this is some sort of secondary interrupt controller, cascaded into
> your GIC emulation,
    
I guess it could be seen as a secondary interrupt controller


> and this patch only affects the xen_dynamic_chip?

Yep
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