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Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with platform legacy quirk

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On 04/08/2016 02:29 AM, 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:
>>> On Thu, Apr 07, 2016 at 08:55:54AM -0400, Boris Ostrovsky wrote:
>>>> On 04/06/2016 08:06 PM, Luis R. Rodriguez wrote:
>>>>> We have 4 types of x86 platforms that disable RTC:
>>>>>
>>>>>    * Intel MID
>>>>>    * Lguest - uses paravirt
>>>>>    * Xen dom-U - uses paravirt
>>>>>    * x86 on legacy systems annotated with an ACPI legacy flag
>>>>>
>>>>> We can consolidate all of these into a platform specific legacy
>>>>> quirk set early in boot through i386_start_kernel() and through
>>>>> x86_64_start_reservations(). This deals with the RTC quirks which
>>>>> we can rely on through the hardware subarch, the ACPI check can
>>>>> be dealt with separately.
>>>>>
>>>>> v2: split the subarch check from the ACPI check, clarify
>>>>>      on the ACPI change commit log why ordering works
>>>>>
>>>>> Suggested-by: Ingo Molnar <mingo@kernel.org>
>>>>> Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
>>> <-- snip -->
>>>
>>>>> diff --git a/arch/x86/kernel/platform-quirks.c b/arch/x86/kernel/platform-quirks.c
>>>>> new file mode 100644
>>>>> index 000000000000..1b114ac5996f
>>>>> --- /dev/null
>>>>> +++ b/arch/x86/kernel/platform-quirks.c
>>>>> @@ -0,0 +1,18 @@
>>>>> +#include <linux/kernel.h>
>>>>> +#include <linux/init.h>
>>>>> +
>>>>> +#include <asm/setup.h>
>>>>> +#include <asm/bios_ebda.h>
>>>>> +
>>>>> +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;
>>>>> +           break;
>>>>> +   }
>>>>> +}
>>>> What about Xen dom0 (aka initial domain)?
>>> Indeed, thanks for catching this, the hunk below removes the re-enablement of
>>> the the RTC for dom0:
>>>
>>>>> --- a/arch/x86/xen/enlighten.c
>>>>> +++ b/arch/x86/xen/enlighten.c
>>>>> @@ -1192,7 +1192,6 @@ static const struct pv_info xen_info __initconst = {
>>>>>   #ifdef CONFIG_X86_64
>>>>>      .extra_user_64bit_cs = FLAT_USER_CS64,
>>>>>   #endif
>>>>> -   .features = 0,
>>>>>      .name = "Xen",
>>>>>   };
>>>>> @@ -1525,8 +1524,6 @@ asmlinkage __visible void __init xen_start_kernel(void)
>>>>>      /* Install Xen paravirt ops */
>>>>>      pv_info = xen_info;
>>>>> -   if (xen_initial_domain())
>>>>> -           pv_info.features |= PV_SUPPORTED_RTC;
>>>>>      pv_init_ops = xen_init_ops;
>>>>>      if (!xen_pvh_domain()) {
>>>>>              pv_cpu_ops = xen_cpu_ops;
>>> This should then break dom0 unless of course you have the respective next
>>> patch applied and that disabled the RTC due to an ACPI setting on your
>>> platform. Juergen, can you check to see if that was the case for your
>>> testing platform on dom0 ?
>> Are you sure it would break?
> No, suspected that it should though.
>
>> Wouldn't it just fall back to another
>> clock source, e.g. hpet?
> I suppose so.
>
>> I looked into my test system: seems as if add_rtc_cmos() is returning
>> before the .legacy.rtc test.
> OK thanks...

It works because the clock must have been discovered by ACPI prior to 
add_rtc_cmos() call. It's PNP0b00 object, I believe. The rest of the 
routine is to handle the case when RTC is not found in ACPI tables for 
whatever reasons (I think).

That's why we added paravirt_has(RTC) --- dom0 should be able to handle 
such cases, just like bare metal.

-boris

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[PATCH v4 00/14] x86: remove paravirt_enabled "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 06/14] x86/init: use a platform legacy quirk for ebda "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
    Re: [Xen-devel] [PATCH v4 06/14] x86/init: use a platform legacy  quirk for ebda David Vrabel <david.vrabel@citrix.com> - 2016-04-07 11:50 +0200
      Re: [Xen-devel] [PATCH v4 06/14] x86/init: use a platform legacy  quirk for ebda "Luis R. Rodriguez" <mcgrof@suse.com> - 2016-04-07 23:10 +0200
  [PATCH v4 10/14] x86/cpu/intel: remove not needed paravirt_enabled() for f00f work around "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 14/14] x86/paravirt: remove paravirt_enabled() "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 13/14] x86/init: rename ebda code file "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
    Re: [Xen-devel] [PATCH v4 04/14] x86/rtc: replace paravirt rtc check  with platform legacy quirk David Vrabel <david.vrabel@citrix.com> - 2016-04-07 11:50 +0200
      Re: [Xen-devel] [PATCH v4 04/14] x86/rtc: replace paravirt rtc check  with platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-14 01:10 +0200
    Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-07 15:00 +0200
      Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 02:40 +0200
        Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Juergen Gross <jgross@suse.com> - 2016-04-08 07:20 +0200
          Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Juergen Gross <jgross@suse.com> - 2016-04-08 08:40 +0200
            Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 09:00 +0200
              Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Juergen Gross <jgross@suse.com> - 2016-04-08 09:20 +0200
                Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 09:40 +0200
                Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Juergen Gross <jgross@suse.com> - 2016-04-08 10:10 +0200
                Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-08 14:40 +0200
                Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 20:50 +0200
          Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 08:40 +0200
            Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-08 14:30 +0200
  [PATCH v4 07/14] tools/lguest: force disable tboot and apm "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
    Re: [PATCH v4 07/14] tools/lguest: force disable tboot and apm Rusty Russell <rusty@rustcorp.com.au> - 2016-04-11 06:00 +0200
  [PATCH v4 03/14] tools/lguest: make lguest launcher use X86_SUBARCH_LGUEST explicitly "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 08/14] apm32: remove paravirt_enabled() use "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
    Re: [PATCH v4 08/14] apm32: remove paravirt_enabled() use Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-07 15:10 +0200
      Re: [PATCH v4 08/14] apm32: remove paravirt_enabled() use "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 00:40 +0200
  [PATCH v4 12/14] x86, ACPI: parse ACPI_FADT_LEGACY_DEVICES "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 01/14] x86/boot: enumerate documentation for the x86 hardware_subarch "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
    Re: [PATCH v4 01/14] x86/boot: enumerate documentation for the x86  hardware_subarch Andy Shevchenko <andriy.shevchenko@linux.intel.com> - 2016-04-07 13:30 +0200
      Re: [PATCH v4 01/14] x86/boot: enumerate documentation for the x86  hardware_subarch "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 00:40 +0200
  [PATCH v4 09/14] x86/tboot: remove paravirt_enabled() "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 02/14] x86/xen: use X86_SUBARCH_XEN for PV guest boots "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:20 +0200
    Re: [Xen-devel] [PATCH v4 02/14] x86/xen: use X86_SUBARCH_XEN for PV  guest boots David Vrabel <david.vrabel@citrix.com> - 2016-04-07 11:50 +0200
  [PATCH v4 05/14] x86, ACPI: move ACPI_FADT_NO_CMOS_RTC check to ACPI boot code "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:20 +0200
  Re: [Xen-devel] [PATCH v4 00/14] x86: remove paravirt_enabled Juergen Gross <jgross@suse.com> - 2016-04-07 15:30 +0200
  [PATCH v4 13/14] x86/init: rename ebda code file "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 23:40 +0200
  Re: [PATCH v4 00/14] x86: remove paravirt_enabled "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 03:20 +0200
    Re: [PATCH v4 00/14] x86: remove paravirt_enabled Borislav Petkov <bp@alien8.de> - 2016-04-08 12:30 +0200

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