Subject: Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with
 platform legacy quirk
To: "Luis R. Rodriguez" <mcgrof@kernel.org>
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Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        Rusty Russell <rusty@rustcorp.com.au>, X86 ML <x86@kernel.org>,
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        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Joey Lee <jlee@suse.com>, Gary Lin <glin@suse.com>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>, Len Brown <lenb@kernel.org>,
        "Moore, Robert" <robert.moore@intel.com>,
        Lv Zheng <lv.zheng@intel.com>, Toshi Kani <toshi.kani@hp.com>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        kozerkov@parallels.com, Josh Triplett <josh@joshtriplett.org>,
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From: Juergen Gross <jgross@suse.com>
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Date: Fri, 8 Apr 2016 08:38:57 +0200
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On 08/04/16 08:29, Luis R. Rodriguez wrote:
> On Thu, Apr 7, 2016 at 10:18 PM, Juergen Gross <jgross@suse.com> wrote:
>> On 08/04/16 02:32, Luis R. Rodriguez wrote:
>>> This highlights a semantic gap issue. From a quick cursory review, I think
>>> we can address this temporarily by just using a check:
>>>
>>> void __init x86_early_init_platform_quirks(void)
>>> {
>>>       x86_platform.legacy.rtc = 1;
>>>
>>>       switch (boot_params.hdr.hardware_subarch) {
>>>       case X86_SUBARCH_XEN:
>>>       case X86_SUBARCH_LGUEST:
>>>       case X86_SUBARCH_INTEL_MID:
>>> -             x86_platform.legacy.rtc = 0;
>>> +             if (x86_init.mpparse.get_smp_config != x86_init_uint_noop)
>>> +                     x86_platform.legacy.rtc = 0;
>>
>> No! Why don't you just use the explicit test xen_initial_domain() ?
> 
> Because we don't want to sprinkle Xen specific code outside of Xen
> code. What do you think about the second possibility I listed?
> Otherwise, any other ideas?

Don't try to guess.

In case you don't want to inject Xen internals here, just call a Xen
function to either return the correct value, or to set all structure
elements correctly.

Thinking more about it: why not do that for all the subarchs? You'd
have the specific settings where they belong: in a subarch specific
source. Just do the default settings in x86_early_init_platform_quirks()
and let the subarch functions set the non-default values.


Juergen