linux-kernel - [PATCH 1/2] RISC-V: Cache SBI vendor values

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Message-Id: <20221004203724.1459763-2-heiko@sntech.de>
Date:   Tue,  4 Oct 2022 22:37:23 +0200
From:   Heiko Stuebner <heiko@...ech.de>
To:     atishp@...shpatra.org, anup@...infault.org, will@...nel.org,
        mark.rutland@....com, paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Conor.Dooley@...rochip.com, cmuellner@...ux.com,
        samuel@...lland.org, Heiko Stuebner <heiko@...ech.de>
Subject: [PATCH 1/2] RISC-V: Cache SBI vendor values

sbi_get_mvendorid(), sbi_get_marchid() and sbi_get_mimpid() might get
called multiple times, though the values of these CSRs should not change
during the runtime of a specific machine.

So cache the values in the functions and prevent multiple ecalls
to read these values.

Suggested-by: Atish Patra <atishp@...shpatra.org>
Signed-off-by: Heiko Stuebner <heiko@...ech.de>
---
 arch/riscv/kernel/sbi.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
index 775d3322b422..5be8f90f325e 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -625,17 +625,32 @@ static inline long sbi_get_firmware_version(void)
 
 long sbi_get_mvendorid(void)
 {
-	return __sbi_base_ecall(SBI_EXT_BASE_GET_MVENDORID);
+	static long id = -1;
+
+	if (id < 0)
+		id = __sbi_base_ecall(SBI_EXT_BASE_GET_MVENDORID);
+
+	return id;
 }
 
 long sbi_get_marchid(void)
 {
-	return __sbi_base_ecall(SBI_EXT_BASE_GET_MARCHID);
+	static long id = -1;
+
+	if (id < 0)
+		id = __sbi_base_ecall(SBI_EXT_BASE_GET_MARCHID);
+
+	return id;
 }
 
 long sbi_get_mimpid(void)
 {
-	return __sbi_base_ecall(SBI_EXT_BASE_GET_MIMPID);
+	static long id = -1;
+
+	if (id < 0)
+		id = __sbi_base_ecall(SBI_EXT_BASE_GET_MIMPID);
+
+	return id;
 }
 
 static void sbi_send_cpumask_ipi(const struct cpumask *target)
-- 
2.35.1