linux-kernel - Re: [Xen-devel] [PATCHv1] x86: rtc_cmos platform device requires legacy irqs

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Date:	Fri, 4 Dec 2015 11:14:09 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:	David Vrabel <david.vrabel@...rix.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, xen-devel@...ts.xenproject.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Xen-devel] [PATCHv1] x86: rtc_cmos platform device requires
 legacy irqs

On 12/04/2015 10:52 AM, Vitaly Kuznetsov wrote:
> Boris Ostrovsky <boris.ostrovsky@...cle.com> writes:
>
>> On 12/04/2015 10:24 AM, David Vrabel wrote:
>>> On 04/12/15 14:06, David Vrabel wrote:
>>>> On 03/12/15 10:43, David Vrabel wrote:
>>>>> Adding the rtc platform device when there are no legacy irqs (no
>>>>> legacy PIC) causes a conflict with other devices that end up using the
>>>>> same irq number.
>>>> An alternative is to remove the rtc_cmos platform device in Xen PV
>>>> guests.
>>>>
>>>> Any preference on how this regression should be fixed?
>>>>
>>>> David
>>>>
>>>> 8<--------------------------
>>>> x86: Xen PV guests don't have the rtc_cmos platform device
>>>>
>>> [...]
>>>> --- a/arch/x86/kernel/rtc.c
>>>> +++ b/arch/x86/kernel/rtc.c
>>>> @@ -200,6 +200,9 @@ static __init int add_rtc_cmos(void)
>>>>    	}
>>>>    #endif
>>>>    +	if (xen_pv_domain())
>>>> +		return -ENODEV;
>>>> +
>>> Note there's a missing include that breaks !XEN builds.
>> We could also use paravirt_enable() here which will probably cover
>> HVMlite case as well. (Until we start turning on and off various
>> HVMlite features).
> Would it make sense to create a new abstraction, e.g. 'rtc_available' in
> struct hypervisor_x86?

We could do this but since this fine-grained feature enabling is still 
way off it may be worth waiting until we actually get to this.

Besides, it would probably be something like if (paravirt_enabled() && 
!rtc_available) so for now having just the first term should suffice.

-boris
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