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Re: [PATCH v4 05/15] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline
- To: "Penny, Zheng" <penny.zheng@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 12 May 2025 18:02:26 +0200
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- Cc: "Huang, Ray" <Ray.Huang@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, "Orzel, Michal" <Michal.Orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 12 May 2025 16:02:33 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 07.05.2025 07:27, Penny, Zheng wrote:
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@xxxxxxxx>
>> Sent: Tuesday, April 29, 2025 8:52 PM
>>
>> On 14.04.2025 09:40, Penny Zheng wrote:
>>> @@ -573,6 +576,14 @@ ret_t do_platform_op(
>>> }
>>>
>>> case XEN_PM_CPPC:
>>> + if ( !(xen_processor_pmbits & XEN_PROCESSOR_PM_CPPC) )
>>> + {
>>> + ret = -EOPNOTSUPP;
>>> + break;
>>> + }
>>
>> While at least you no longer use -ENOSYS here, I question this behavior,
>> including
>> that for the pre-existing cases: How is the caller supposed to know whether
>> to
>> invoke this sub-op? Ignoring errors is generally not a good idea, so it
>> would be
>> better if the caller could blindly issue this request, getting back success
>> unless
>> there really was an issue with the data provided.
>>
>
> Understood.
> I will change it to ret = 0. Do you think we shall add warning info here?
No, for precisely ...
> Dom0 will send the CPPC data whenever it could.
... this reason.
Jan
> XEN_PROCESSOR_PM_CPPC
> is not set could largely be users choosing not to. In such case, silently
> getting back success
> shall be enough.
>
>
>> Jan
|
