[tip: perf/core] perf/x86/intel/p4: Fix unused variable warning in p4_pmu_init()

[tip-bot2 for Aldo Conte]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     6ee26b7a224b27aa7e8e1ee8a845a31664d2e97c
Gitweb:        https://git.kernel.org/tip/6ee26b7a224b27aa7e8e1ee8a845a31664d2e97c
Author:        Aldo Conte <aldocontelk@xxxxxxxxx>
AuthorDate:    Fri, 20 Mar 2026 12:23:02 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 24 Mar 2026 15:11:42 +01:00

perf/x86/intel/p4: Fix unused variable warning in p4_pmu_init()

Build the kernel with make W=1 generates the following warning:

  arch/x86/events/intel/p4.c: In function ‘p4_pmu_init’:
  arch/x86/events/intel/p4.c:1370:27: error: variable ‘high’ set but not used [-Werror=unused-but-set-variable]
   1370 |         unsigned int low, high;
        |                           ^~~~

This happens because, although both variables are declared and
initialized by rdmsr, only `low` is used in the subsequent if statement.

This patch uses the rdmsrq() macro instead of the rdmsr() macro.
The rdmsrq() macro avoids the use of high and low variables
because it reads the msr value in a single u64 variable.
Also, replace (1 << 7) with the proper macro.

Running `make W=1` again resolves the error.
I was unable to test the patch because
i do not have the hardware.

Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Aldo Conte <aldocontelk@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://patch.msgid.link/20260320112302.281549-1-aldocontelk@xxxxxxxxx
---
 arch/x86/events/intel/p4.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/events/intel/p4.c b/arch/x86/events/intel/p4.c
index e5fd736..02bfdb7 100644
--- a/arch/x86/events/intel/p4.c
+++ b/arch/x86/events/intel/p4.c
@@ -1367,14 +1367,14 @@ static __initconst const struct x86_pmu p4_pmu = {
 
 __init int p4_pmu_init(void)
 {
-	unsigned int low, high;
+	unsigned int misc;
 	int i, reg;
 
 	/* If we get stripped -- indexing fails */
 	BUILD_BUG_ON(ARCH_P4_MAX_CCCR > INTEL_PMC_MAX_GENERIC);
 
-	rdmsr(MSR_IA32_MISC_ENABLE, low, high);
-	if (!(low & (1 << 7))) {
+	rdmsrq(MSR_IA32_MISC_ENABLE, misc);
+	if (!(misc & MSR_IA32_MISC_ENABLE_EMON)) {
 		pr_cont("unsupported Netburst CPU model %d ",
 			boot_cpu_data.x86_model);
 		return -ENODEV;