linux-kernel - [PATCH 2/5] riscv: nommu: use CSR_TIME* for get

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Date: Tue, 26 Mar 2024 00:40:18 +0800
From: Jisheng Zhang <jszhang@...nel.org>
To: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] riscv: nommu: use CSR_TIME* for get_cycles* implementation

Per riscv privileged spec, "The time CSR is a read-only shadow of the
memory-mapped mtime register", "On RV32I the timeh CSR is a read-only
shadow of the upper 32 bits of the memory-mapped mtime register, while
time shadows only the lower 32 bits of mtime." Since get_cycles() only
reads the timer, it's fine to use CSR_TIME to implement get_cycles().

Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
---
 arch/riscv/include/asm/timex.h | 40 ----------------------------------
 1 file changed, 40 deletions(-)

diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
index a06697846e69..a3fb85d505d4 100644
--- a/arch/riscv/include/asm/timex.h
+++ b/arch/riscv/include/asm/timex.h
@@ -10,44 +10,6 @@
 
 typedef unsigned long cycles_t;
 
-#ifdef CONFIG_RISCV_M_MODE
-
-#include <asm/clint.h>
-
-#ifdef CONFIG_64BIT
-static inline cycles_t get_cycles(void)
-{
-	return readq_relaxed(clint_time_val);
-}
-#else /* !CONFIG_64BIT */
-static inline u32 get_cycles(void)
-{
-	return readl_relaxed(((u32 *)clint_time_val));
-}
-#define get_cycles get_cycles
-
-static inline u32 get_cycles_hi(void)
-{
-	return readl_relaxed(((u32 *)clint_time_val) + 1);
-}
-#define get_cycles_hi get_cycles_hi
-#endif /* CONFIG_64BIT */
-
-/*
- * Much like MIPS, we may not have a viable counter to use at an early point
- * in the boot process. Unfortunately we don't have a fallback, so instead
- * we just return 0.
- */
-static inline unsigned long random_get_entropy(void)
-{
-	if (unlikely(clint_time_val == NULL))
-		return random_get_entropy_fallback();
-	return get_cycles();
-}
-#define random_get_entropy()	random_get_entropy()
-
-#else /* CONFIG_RISCV_M_MODE */
-
 static inline cycles_t get_cycles(void)
 {
 	return csr_read(CSR_TIME);
@@ -60,8 +22,6 @@ static inline u32 get_cycles_hi(void)
 }
 #define get_cycles_hi get_cycles_hi
 
-#endif /* !CONFIG_RISCV_M_MODE */
-
 #ifdef CONFIG_64BIT
 static inline u64 get_cycles64(void)
 {
-- 
2.43.0