[Bug 220715] [REGRESSION] AMD P-State fails with "_CPC object is not present" on AMD Zen 4 between 6.10 and 6.11

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=220715

Gautham R. Shenoy (gautham.shenoy@gmail.com) changed:

           What    |Removed                     |Added
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                 CC|                            |gautham.shenoy@gmail.com

--- Comment #16 from Gautham R. Shenoy (gautham.shenoy@gmail.com) ---
I think Mario is on the right track in that the issue is because of failure to
detect something on a CPU that is present but not online.

My hunch is that it is in amd_detect_prefcore() which checks if the number of
distinct highest_perf values in the system is greater than 1, but uses
for_each_present_cpu() which fails when the system is booted with
`nosmt=force`. The commit that introduces this code is 279f838a61f9  ("x86/amd:
Detect preferred cores in amd_get_boost_ratio_numerator()") which got merged in
the upstream kernel 6.12.


@Chris, if you don't mind, can you please try the following patch:

diff --git a/arch/x86/kernel/acpi/cppc.c b/arch/x86/kernel/acpi/cppc.c
index 7047124490f6..d7c8ef1e354d 100644
--- a/arch/x86/kernel/acpi/cppc.c
+++ b/arch/x86/kernel/acpi/cppc.c
@@ -196,7 +196,7 @@ int amd_detect_prefcore(bool *detected)
                break;
        }

-       for_each_present_cpu(cpu) {
+       for_each_online_cpu(cpu) {
                u32 tmp;
                int ret;

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