acpi: Tell SMM we will handle CPPC notifications

Buggy SMM implementations can hang while processing CPPC notifications.
This leads to some laptops (notably Thinkpads) hanging when the
hwpstate_intel driver is loaded.

Tell the SMM that we will handle CPPC notifications as described in:

- Intel® Processor Vendor-Specific ACPI
- Intel® 64 and IA-32 Architectures Software Developer’s Manual

CPPC events default to masked (disabled) so while we do not do any
handling right now this does not seem to lead to any issues.

This approach was found via this Linux Kernel patch:
https://lkml.org/lkml/2016/3/17/563

PR:		253288
Reviewed by:	imp, jhb
Sponsored by:	Modirum
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D36699

1 files changed, 14 insertions, 0 deletions

diff --git a/sys/dev/acpica/acpi_cpu.c b/sys/dev/acpica/acpi_cpu.c
index 762ea37cfa34..49d2bd11fdaa 100644
--- a/sys/dev/acpica/acpi_cpu.c
+++ b/sys/dev/acpica/acpi_cpu.c
@@ -153,6 +153,7 @@ static struct sysctl_ctx_list cpu_sysctl_ctx;
 static struct sysctl_oid *cpu_sysctl_tree;
 static int		 cpu_cx_generic;
 static int		 cpu_cx_lowest_lim;
+static bool		 cppc_notify;
 
 static struct acpi_cpu_softc **cpu_softc;
 ACPI_SERIAL_DECL(cpu, "ACPI CPU");
@@ -396,6 +397,13 @@ acpi_cpu_attach(device_t dev)
      */
     if (!acpi_disabled("mwait") && cpu_mwait_usable())
 	sc->cpu_features |= ACPI_CAP_SMP_C1_NATIVE | ACPI_CAP_SMP_C3_NATIVE;
+
+    /*
+     * Work around a lingering SMM bug which leads to freezes when handling
+     * CPPC notifications. Tell the SMM we will handle any CPPC notifications.
+     */
+    if ((cpu_power_eax & CPUTPM1_HWP_NOTIFICATION) && cppc_notify)
+	    sc->cpu_features |= ACPI_CAP_INTR_CPPC;
 #endif
 
     if (devclass_get_drivers(device_get_devclass(dev), &drivers,
@@ -977,6 +985,12 @@ acpi_cpu_startup(void *arg)
 	NULL, 0, acpi_cpu_global_cx_lowest_sysctl, "A",
 	"Global lowest Cx sleep state to use");
 
+    /* Add sysctl handler to control registering for CPPC notifications */
+    cppc_notify = 1;
+    SYSCTL_ADD_BOOL(&cpu_sysctl_ctx, SYSCTL_CHILDREN(cpu_sysctl_tree),
+	OID_AUTO, "cppc_notify", CTLFLAG_RDTUN | CTLFLAG_MPSAFE,
+	&cppc_notify, 0, "Register for CPPC Notifications");
+
     /* Take over idling from cpu_idle_default(). */
     cpu_cx_lowest_lim = 0;
     CPU_FOREACH(i) {