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Re: [PATCH 04/13] cpufreq: Add Hardware P-State (HWP) driver
- To: Jason Andryuk <jandryuk@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 4 Jun 2021 08:39:12 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 04 Jun 2021 06:39:21 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 03.06.2021 13:55, Jason Andryuk wrote:
> On Fri, May 28, 2021 at 2:35 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> On 27.05.2021 20:50, Jason Andryuk wrote:
>>> On Wed, May 26, 2021 at 11:00 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>>> On 03.05.2021 21:28, Jason Andryuk wrote:
>>>>> + hwp_verbose("HWP: FAST_IA32_HWP_REQUEST %ssupported\n",
>>>>> + eax & CPUID6_EAX_FAST_HWP_MSR ? "" : "not ");
>>>>> + if ( eax & CPUID6_EAX_FAST_HWP_MSR )
>>>>> + {
>>>>> + if ( rdmsr_safe(MSR_FAST_UNCORE_MSRS_CAPABILITY, val) )
>>>>> + hwp_err("error
>>>>> rdmsr_safe(MSR_FAST_UNCORE_MSRS_CAPABILITY)\n");
>>>>> +
>>>>> + hwp_verbose("HWP: MSR_FAST_UNCORE_MSRS_CAPABILITY: %016lx\n",
>>>>> val);
>>>>
>>>> Missing "else" above here?
>>>
>>> Are unbalanced braces acceptable or must they be balanced? Is this
>>> acceptable:
>>> if ()
>>> one;
>>> else {
>>> two;
>>> three;
>>> }
>>
>> Yes, it is. But I don't see how the question relates to my comment.
>> All that needs to go in the else's body is the hwp_verbose().
>
> 'val' shouldn't be used to set features when the rdmsr fails, so the
> following code needs to be within the else. Unless you want to rely
> on a failed rdmsr returning 0.
It is intentional for rdmsr_safe() to return a zero value when the
access faulted, so I certainly think you may rely on this.
Jan
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