cpu: New cpu_get_pcpuid(), retrieves internal CPU ID

It is a handy shortcut that will be used extensively in
hwpstate_intel(4) and hwpstate_amd(4).

Warn users that it panics if the parent bus does not provide the
CPU_IVAR_PCPU instance variable.  That condition should be tested by
callers (doing so once is enough).  Suggest to do that in driver's
attach method.

Reviewed by:    jhb (code)
Event:          Halifax Hackathon 202606
Location:       Seat 36K in AC667, waiting for a gate at Montréal-Trudeau
Sponsored by:   The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D57897

1 files changed, 11 insertions, 0 deletions

diff --git a/sys/sys/cpu.h b/sys/sys/cpu.h
index 21e79e6db6a4..9156fa9f723d 100644
--- a/sys/sys/cpu.h
+++ b/sys/sys/cpu.h
@@ -51,6 +51,17 @@ cpu_get_pcpu(device_t dev)
 	return ((struct pcpu *)v);
 }
 
+/*
+ * Assumes the parent bus sets the CPU_IVAR_PCPU instance variable, which most
+ * CPU buses do.  A panic will ensure if not the case.  Calling devices should
+ * check for that condition (most probably in their attach function).
+ */
+static __inline u_int
+cpu_get_pcpuid(device_t dev)
+{
+	return (cpu_get_pcpu(dev)->pc_cpuid);
+}
+
 static __inline int32_t
 cpu_get_nominal_mhz(device_t dev)
 {