[tip: x86/cpu] x86/acpi/cstate: Optimize ARB_DISABLE on Centaur CPUs

[tip-bot2 for Tony W Wang-oc]

The following commit has been merged into the x86/cpu branch of tip:

Commit-ID:     dacca1e5e75d7c1297f1334cdc10491dcdd1b2b8
Gitweb:        https://git.kernel.org/tip/dacca1e5e75d7c1297f1334cdc10491dcdd1b2b8
Author:        Tony W Wang-oc <TonyWWang-oc@xxxxxxxxxxx>
AuthorDate:    Mon, 07 Nov 2022 11:34:49 +08:00
Committer:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Fri, 11 Nov 2022 09:42:05 -08:00

x86/acpi/cstate: Optimize ARB_DISABLE on Centaur CPUs

On all recent Centaur platforms, ARB_DISABLE is handled by PMU
automatically while entering C3 type state. No need for OS to
issue the ARB_DISABLE, so set bm_control to zero to indicate that.

Signed-off-by: Tony W Wang-oc <TonyWWang-oc@xxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Link: https://lore.kernel.org/all/1667792089-4904-1-git-send-email-TonyWWang-oc%40zhaoxin.com
---
 arch/x86/kernel/acpi/cstate.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
index 7945eae..401808b 100644
--- a/arch/x86/kernel/acpi/cstate.c
+++ b/arch/x86/kernel/acpi/cstate.c
@@ -52,17 +52,25 @@ void acpi_processor_power_init_bm_check(struct acpi_processor_flags *flags,
 	if (c->x86_vendor == X86_VENDOR_INTEL &&
 	    (c->x86 > 0xf || (c->x86 == 6 && c->x86_model >= 0x0f)))
 			flags->bm_control = 0;
-	/*
-	 * For all recent Centaur CPUs, the ucode will make sure that each
-	 * core can keep cache coherence with each other while entering C3
-	 * type state. So, set bm_check to 1 to indicate that the kernel
-	 * doesn't need to execute a cache flush operation (WBINVD) when
-	 * entering C3 type state.
-	 */
+
 	if (c->x86_vendor == X86_VENDOR_CENTAUR) {
 		if (c->x86 > 6 || (c->x86 == 6 && c->x86_model == 0x0f &&
-		    c->x86_stepping >= 0x0e))
+		    c->x86_stepping >= 0x0e)) {
+			/*
+			 * For all recent Centaur CPUs, the ucode will make sure that each
+			 * core can keep cache coherence with each other while entering C3
+			 * type state. So, set bm_check to 1 to indicate that the kernel
+			 * doesn't need to execute a cache flush operation (WBINVD) when
+			 * entering C3 type state.
+			 */
 			flags->bm_check = 1;
+			/*
+			 * For all recent Centaur platforms, ARB_DISABLE is a nop.
+			 * Set bm_control to zero to indicate that ARB_DISABLE is
+			 * not required while entering C3 type state.
+			 */
+			flags->bm_control = 0;
+		}
 	}
 
 	if (c->x86_vendor == X86_VENDOR_ZHAOXIN) {