workaround Intel Braswell/Cherry Trail mwait hang

dlg has a Dell Wyse 3040 with
cpu0: Intel(R) Atom(TM) x5-Z8350 CPU @ 1.44GHz, 480.02 MHz, 06-4c-04
cpu0: mwait min=64, max=64, C-substates=0.2.0.0.0.0.3.3, IBE
which hangs soon after the login prompt with MP kernels

This is a hardware bug described in:
Intel Atom Z8000 Processor Series Specification Update
Document Number: 332067-012
"CHT45 Processor May Not Wake From C6 or Deeper Sleep State"

tested by dlg@, ok guenther@

diff --git a/sys/arch/amd64/amd64/cpu.c b/sys/arch/amd64/amd64/cpu.c
index 38efd28..418ed9a 100644 (file)
--- a/sys/arch/amd64/amd64/cpu.c
+++ b/sys/arch/amd64/amd64/cpu.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: cpu.c,v 1.164 2023/01/20 16:01:04 deraadt Exp $       */
+/*     $OpenBSD: cpu.c,v 1.165 2023/03/09 13:17:28 jsg Exp $   */
 /* $NetBSD: cpu.c,v 1.1 2003/04/26 18:39:26 fvdl Exp $ */
 
 /*-
@@ -433,7 +433,7 @@ cpu_match(struct device *parent, void *match, void *aux)
 }
 
 void   cpu_idle_mwait_cycle(void);
-void   cpu_init_mwait(struct cpu_softc *);
+void   cpu_init_mwait(struct cpu_softc *, struct cpu_info *);
 
 u_int  cpu_mwait_size, cpu_mwait_states;
 
@@ -471,7 +471,7 @@ cpu_idle_mwait_cycle(void)
 }
 
 void
-cpu_init_mwait(struct cpu_softc *sc)
+cpu_init_mwait(struct cpu_softc *sc, struct cpu_info *ci)
 {
        unsigned int smallest, largest, extensions, c_substates;
 
@@ -483,6 +483,11 @@ cpu_init_mwait(struct cpu_softc *sc)
        smallest &= 0xffff;
        largest  &= 0xffff;
 
+       /* mask out states C6/C7 in 31:24 for CHT45 errata */
+       if (strcmp(cpu_vendor, "GenuineIntel") == 0 &&
+           ci->ci_family == 0x06 && ci->ci_model == 0x4c)
+               cpu_mwait_states &= 0x00ffffff;
+
        printf("%s: mwait min=%u, max=%u", sc->sc_dev.dv_xname,
            smallest, largest);
        if (extensions & 0x1) {
@@ -620,7 +625,7 @@ cpu_attach(struct device *parent, struct device *self, void *aux)
 #endif /* MTRR */
                /* XXX SP fpuinit(ci) is done earlier */
                cpu_init(ci);
-               cpu_init_mwait(sc);
+               cpu_init_mwait(sc, ci);
                break;
 
        case CPU_ROLE_BP:
@@ -647,7 +652,7 @@ cpu_attach(struct device *parent, struct device *self, void *aux)
 #if NIOAPIC > 0
                ioapic_bsp_id = caa->cpu_apicid;
 #endif
-               cpu_init_mwait(sc);
+               cpu_init_mwait(sc, ci);
                break;
 
        case CPU_ROLE_AP: