linux-kernel - [PATCH] arm64: cpufeature: Expose the real mpidr value to EL0

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Message-Id: <20230912035209.1687-1-guojinhui.liam@bytedance.com>
Date:   Tue, 12 Sep 2023 11:52:09 +0800
From:   "guojinhui.liam" <guojinhui.liam@...edance.com>
To:     catalin.marinas@....com, will@...nel.org
Cc:     lizefan.x@...edance.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        "guojinhui.liam" <guojinhui.liam@...edance.com>
Subject: [PATCH] arm64: cpufeature: Expose the real mpidr value to EL0

In EL0, it can get the register midr's value to distinguish vendor.
But it won't return real value of the register mpidr by using mrs
in EL0. The register mpidr's value is useful to obtain the cpu
topology information.

In some scenarios, the task scheduling in userspace can be
optimized with CPU Die information.

Signed-off-by: guojinhui.liam <guojinhui.liam@...edance.com>
---
 arch/arm64/include/asm/sysreg.h | 3 ---
 arch/arm64/kernel/cpufeature.c  | 2 +-
 2 files changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 38296579a4fd..1885857c8a22 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -901,9 +901,6 @@
 #define SYS_TFSR_EL1_TF0	(UL(1) << SYS_TFSR_EL1_TF0_SHIFT)
 #define SYS_TFSR_EL1_TF1	(UL(1) << SYS_TFSR_EL1_TF1_SHIFT)
 
-/* Safe value for MPIDR_EL1: Bit31:RES1, Bit30:U:0, Bit24:MT:0 */
-#define SYS_MPIDR_SAFE_VAL	(BIT(31))
-
 #define TRFCR_ELx_TS_SHIFT		5
 #define TRFCR_ELx_TS_MASK		((0x3UL) << TRFCR_ELx_TS_SHIFT)
 #define TRFCR_ELx_TS_VIRTUAL		((0x1UL) << TRFCR_ELx_TS_SHIFT)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index b018ae12ff5f..6e18597fdcc3 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -3450,7 +3450,7 @@ static inline int emulate_id_reg(u32 id, u64 *valp)
 		*valp = read_cpuid_id();
 		break;
 	case SYS_MPIDR_EL1:
-		*valp = SYS_MPIDR_SAFE_VAL;
+		*valp = read_cpuid_mpidr();
 		break;
 	case SYS_REVIDR_EL1:
 		/* IMPLEMENTATION DEFINED values are emulated with 0 */
-- 
2.20.1