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

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Date:	Wed, 18 Jul 2012 17:51:55 +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, 16 Jul 2012, Konrad Rzeszutek Wilk wrote:
> On Fri, Jul 13, 2012 at 06:14:33PM +0100, Stefano Stabellini wrote:
> > 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.
> 
> OK, please include those questions/answers in the git commit and
> repost.

---

xen/arm: enable evtchn irqs

On ARM Linux irqs are not enabled by default:

- call enable_percpu_irq for IRQ_EVTCHN_CALLBACK (drivers are supposed
to call enable_irq after request_irq);

- 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.
This is needed because IRQ_NOAUTOEN is set by set_irq_flags on ARM.
If IRQ_NOAUTOEN is set __setup_irq doesn't call irq_startup that is
responsible for calling irq_unmask at startup time.

Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index eae0d0b..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
@@ -824,6 +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);
@@ -1748,6 +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);
--
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