linux-kernel - Re: [PATCH WIP 6/6] xen/arm: enable evtchn irqs

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Date:	Fri, 13 Jul 2012 18:14:33 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	"Tim (Xen.org)" <tim@....org>
Subject: Re: [PATCH WIP 6/6] xen/arm: enable evtchn irqs

On Mon, 9 Jul 2012, Konrad Rzeszutek Wilk wrote:
> On Fri, Jun 22, 2012 at 05:14:45PM +0100, Stefano Stabellini wrote:
> > On ARM irqs are not enabled by default:
> 
> Which IRQs? Xen IRQs? Linux IRQs?

Linux IRQs


> > - call enable_percpu_irq for IRQ_EVTCHN_CALLBACK;
> 
> Why do we want to do that?
 
drivers are supposed to call enable_irq after request_irq, however on
x86 we could get away without it because Linux irqs are enabled by
default (see below)


> > - set the IRQF_VALID flag for the other irqs bound to evtchns. It causes
> > IRQ_NOAUTOEN to be set and as a consequence irq_unmask is going to be
> > called when a xenbus driver calls request_irq.
> 
> Can you explain in more details why we need that?

If _IRQ_NOAUTOEN is set, irq_settings_can_autoenable returns false and
__setup_irq doesn't call irq_startup.

IRQ_NOAUTOEN is set by default by set_irq_flags on ARM, but not on x86.



> > Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> > ---
> >  drivers/xen/events.c |    3 +++
> >  1 files changed, 3 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> > index 0132505..ca92755 100644
> > --- a/drivers/xen/events.c
> > +++ b/drivers/xen/events.c
> > @@ -53,6 +53,7 @@
> >  #include <xen/interface/hvm/params.h>
> >  #include <xen/interface/physdev.h>
> >  #include <xen/interface/sched.h>
> > +#include <asm/hw_irq.h>
> >  
> >  /*
> >   * This lock protects updates to the following mapping and reference-count
> > @@ -827,6 +828,7 @@ int bind_evtchn_to_irq(unsigned int evtchn)
> >  
> >  		xen_irq_info_evtchn_init(irq, evtchn);
> >  	}
> > +	set_irq_flags(irq, IRQF_VALID);
> >  
> >  out:
> >  	mutex_unlock(&irq_mapping_update_lock);
> > @@ -1751,6 +1753,7 @@ int __init xen_init_IRQ_arm(void)
> >  	if (rc) {
> >  		printk(KERN_ERR "Error requesting IRQ %d\n", IRQ_EVTCHN_CALLBACK);
> >  	}
> > +	enable_percpu_irq(IRQ_EVTCHN_CALLBACK, 0);
> >  	return rc;
> >  }
> >  core_initcall(xen_init_IRQ_arm);
> > -- 
> > 1.7.2.5
> > 
> > --
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