linux-kernel - Re: [PATCH V1] x86/cstate: Add Zhaoxin/Centaur ACPI Cx FFH MWAIT support

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Date:   Fri, 24 Jun 2022 11:05:12 +0800
From:   Tony W Wang-oc <TonyWWang-oc@...oxin.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
CC:     <CobeChen@...oxin.com>, <TimGuo@...oxin.com>,
        <LindaChai@...oxin.com>, <LeoLiu@...oxin.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH V1] x86/cstate: Add Zhaoxin/Centaur ACPI Cx FFH MWAIT
 support

On 23/6/2022 23:55, Dave Hansen wrote:
> On 6/22/22 18:26, Tony W Wang-oc wrote:
>> Recent Zhaoxin/Centaur CPUs support X86_FEATURE_MWAIT that implies
>> the MONITOR/MWAIT instructions can be used for ACPI Cx state.
>> The BIOS declares Cx state in _CST object to use FFH on Zhaoxin/Centaur
>> systems. So let function ffh_cstate_init() support These CPUs too.
>>
>> Signed-off-by: Tony W Wang-oc <TonyWWang-oc@...oxin.com>
>> ---
>>   arch/x86/kernel/acpi/cstate.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
>> index 7945eae..d4185e1 100644
>> --- a/arch/x86/kernel/acpi/cstate.c
>> +++ b/arch/x86/kernel/acpi/cstate.c
>> @@ -213,7 +213,9 @@ static int __init ffh_cstate_init(void)
>>
>>       if (c->x86_vendor != X86_VENDOR_INTEL &&
>>           c->x86_vendor != X86_VENDOR_AMD &&
>> -        c->x86_vendor != X86_VENDOR_HYGON)
>> +        c->x86_vendor != X86_VENDOR_HYGON &&
>> +        c->x86_vendor != X86_VENDOR_CENTAUR &&
>> +        c->x86_vendor != X86_VENDOR_ZHAOXIN)
>>           return -1;
> 
> Many of the changelogs that add new vendors here go on about particular
> C states declared in the _CST object and contents of CPUID leaf 5.
> 
> Why do we even _have_ a vendor check here?  Shouldn't the code just be
> going and doing the validation of the _CST object and CPUID that the
> changelogs blather on about?
> 

Yes, agree!

Will change as below. Please help to check if it is OK. Thanks a lot.
  static int __init ffh_cstate_init(void)
  {
-       struct cpuinfo_x86 *c = &boot_cpu_data;
-
-       if (c->x86_vendor != X86_VENDOR_INTEL &&
-           c->x86_vendor != X86_VENDOR_AMD &&
-           c->x86_vendor != X86_VENDOR_HYGON)
+       if (!boot_cpu_has(X86_FEATURE_MWAIT))
                 return -1;

> Intel certainly made the original sin on this one (see 991528d7348), but
> I hope _something_ changed in the 16 years since that patch went in.
> .
> 

-- 
Sincerely
TonyWWang-oc