Re: [PATCH] x86/MSI: fix guest unmasking when handling IRQ via event channel

From: Julien Grall <julien.grall@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Keir Fraser <keir@xen.org>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	TimDeegan <tim@xen.org>,
	Ian Campbell <Ian.Campbell@eu.citrix.com>,
	SanderEikelenboom <linux@eikelenboom.it>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Ian Jackson <Ian.Jackson@eu.citrix.com>
Subject: Re: [PATCH] x86/MSI: fix guest unmasking when handling IRQ via event channel
Date: Wed, 8 Jul 2015 12:02:31 +0100	[thread overview]
Message-ID: <559D0347.6030604@citrix.com> (raw)
In-Reply-To: <559D1DC0020000780008E1CC@mail.emea.novell.com>

On 08/07/2015 11:55, Jan Beulich wrote:
>>>> On 08.07.15 at 11:07, <julien.grall@citrix.com> wrote:
>> On 08/07/2015 09:56, Jan Beulich wrote:
>>> --- a/xen/include/asm-arm/irq.h
>>> +++ b/xen/include/asm-arm/irq.h
>>> @@ -47,6 +47,8 @@ int release_guest_irq(struct domain *d,
>>>
>>>    void arch_move_irqs(struct vcpu *v);
>>>
>>> +#define arch_evtchn_bind_pirq(d, pirq) ((void)((d) + (pirq)))
>>> +
>>
>> This addition is here in order to ensure that d and pirq are evaluated,
>> right?
>
> Sure.
>
>> If so, I didn't find it obvious to understand. Why didn't you use a
>> static inline? Or maybe add a comment explicitly say this is not
>> implemented.
>
> A static inline could be used in this case, yes. But I see no
> significant advantages. As to the comment - it is implemented,
> it's just a no-op. And stating that it is a no-op would be
> redundant with it obviously being so by looking at it.

It's not so obvious as I asked about it.

The first thing I saw was (d) + (pirq) and I though : "Why do we want to 
add a domain with a pirq?". I only see after the (void) and it just 
because I remembered we talked about similar case a year ago.

Having a comment doesn't hurt and help the comprehension.

-- 
Julien Grall