linux-kernel - [PATCH] x86/acpi/cstate: Delete some unuseful operations for centaur

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Message-ID: <1516701471-25374-1-git-send-email-davidwang@zhaoxin.com>
Date:   Tue, 23 Jan 2018 17:57:51 +0800
From:   davidwang <davidwang@...oxin.com>
To:     <rjw@...ysocki.net>, <len.brown@...el.com>, <pavel@....cz>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>,
        <x86@...nel.org>, <linux-pm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <brucechang@...-alliance.com>, <cooperyan@...oxin.com>,
        <qiyuanwang@...oxin.com>, <benjaminpan@...tech.com>,
        <lukelin@...cpu.com>, <timguo@...oxin.com>, <cobechen@...oxin.com>,
        <jiangbowang@...oxin.com>, <chiachinchu@...cpu.com>,
        davidwang <davidwang@...oxin.com>
Subject: [PATCH] x86/acpi/cstate: Delete some unuseful operations for centaur

For Centaur CPU, the ucode will make sure that each cpu core can keep cache
coherency with each other when the CPU core entering to any C State. So the cache
flush operations when enter C3 is not necessary and will cause large C3 enter/exit
latency.
And the bus master disable operation when CPU core entering C3 state is not needed
too. Because the chipset will automatically do this operation. 
Signed-off-by: davidwang <davidwang@...oxin.com>
---
 arch/x86/kernel/acpi/cstate.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
index dde437f..1cd357b 100644
--- a/arch/x86/kernel/acpi/cstate.c
+++ b/arch/x86/kernel/acpi/cstate.c
@@ -51,6 +51,18 @@ 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;
+
+        if (c->x86_vendor == X86_VENDOR_CENTAUR) {
+		/*
+		 * on all centaur CPUs, sw need not execute cache flush operation
+		 * when entering C3 type State.
+		 *
+		 * On all Centaur platforms, sw need not execute ARB_DISABLE while
+		 * entering C3 type state.
+		 */
+		flags->bm_check = 1;
+		flags->bm_control = 0;
+	}
 }
 EXPORT_SYMBOL(acpi_processor_power_init_bm_check);
 
-- 
1.9.1