linux-kernel - [PATCH] LoongArch: Save and restore CSR.CNTC for hibernation

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Message-ID: <20250514144643.1620870-1-chenhuacai@loongson.cn>
Date: Wed, 14 May 2025 22:46:43 +0800
From: Huacai Chen <chenhuacai@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev,
	Xuefeng Li <lixuefeng@...ngson.cn>,
	Guo Ren <guoren@...nel.org>,
	Xuerui Wang <kernel@...0n.name>,
	Jiaxun Yang <jiaxun.yang@...goat.com>,
	linux-kernel@...r.kernel.org,
	Huacai Chen <chenhuacai@...ngson.cn>,
	stable@...r.kernel.org,
	Xianglai Li <lixianglai@...ngson.cn>
Subject: [PATCH] LoongArch: Save and restore CSR.CNTC for hibernation

Save and restore CSR.CNTC for hibernation which is similar to suspend.

For host this is unnecessary because sched clock is ensured continuous,
but for kvm guest sched clock isn't enough because rdtime.d should also
be continuous.

Host::rdtime.d = Host::CSR.CNTC + counter
Guest::rdtime.d = Host::CSR.CNTC + Host::CSR.GCNTC + Guest::CSR.CNTC + counter

so,

Guest::rdtime.d = Host::rdtime.d + Host::CSR.GCNTC + Guest::CSR.CNTC

To ensure Guest::rdtime.d continuous, Host::rdtime.d should be at first
continuous, while Host::CSR.GCNTC / Guest::CSR.CNTC is maintained by KVM.

Cc: stable@...r.kernel.org
Signed-off-by: Xianglai Li <lixianglai@...ngson.cn>
Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
---
 arch/loongarch/kernel/time.c     | 2 +-
 arch/loongarch/power/hibernate.c | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/kernel/time.c b/arch/loongarch/kernel/time.c
index e2d3bfeb6366..bc75a3a69fc8 100644
--- a/arch/loongarch/kernel/time.c
+++ b/arch/loongarch/kernel/time.c
@@ -111,7 +111,7 @@ static unsigned long __init get_loops_per_jiffy(void)
 	return lpj;
 }
 
-static long init_offset __nosavedata;
+static long init_offset;
 
 void save_counter(void)
 {
diff --git a/arch/loongarch/power/hibernate.c b/arch/loongarch/power/hibernate.c
index 1e0590542f98..e7b7346592cb 100644
--- a/arch/loongarch/power/hibernate.c
+++ b/arch/loongarch/power/hibernate.c
@@ -2,6 +2,7 @@
 #include <asm/fpu.h>
 #include <asm/loongson.h>
 #include <asm/sections.h>
+#include <asm/time.h>
 #include <asm/tlbflush.h>
 #include <linux/suspend.h>
 
@@ -14,6 +15,7 @@ struct pt_regs saved_regs;
 
 void save_processor_state(void)
 {
+	save_counter();
 	saved_crmd = csr_read32(LOONGARCH_CSR_CRMD);
 	saved_prmd = csr_read32(LOONGARCH_CSR_PRMD);
 	saved_euen = csr_read32(LOONGARCH_CSR_EUEN);
@@ -26,6 +28,7 @@ void save_processor_state(void)
 
 void restore_processor_state(void)
 {
+	sync_counter();
 	csr_write32(saved_crmd, LOONGARCH_CSR_CRMD);
 	csr_write32(saved_prmd, LOONGARCH_CSR_PRMD);
 	csr_write32(saved_euen, LOONGARCH_CSR_EUEN);
-- 
2.47.1