linux-kernel - [PATCH RFC 03/12] RISC-V: add Zbb extension detection

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Date:   Mon,  6 Feb 2023 23:58:37 +0100
From:   Heiko Stuebner <heiko@...ech.de>
To:     palmer@...osinc.com
Cc:     greentime.hu@...ive.com, conor@...nel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        christoph.muellner@...ll.eu,
        Heiko Stuebner <heiko.stuebner@...ll.eu>
Subject: [PATCH RFC 03/12] RISC-V: add Zbb extension detection

From: Heiko Stuebner <heiko.stuebner@...ll.eu>

Add handling for Zbb extension.

Zbb provides basic bit-manipulation instructions.

As multiple subsequent features want to check for zbb presence, add the
extension handling without directly including code using it.

Signed-off-by: Heiko Stuebner <heiko.stuebner@...ll.eu>
---
 arch/riscv/Kconfig             | 23 +++++++++++++++++++++++
 arch/riscv/include/asm/hwcap.h |  1 +
 arch/riscv/kernel/cpu.c        |  1 +
 arch/riscv/kernel/cpufeature.c |  1 +
 4 files changed, 26 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index f4299ba9a843..f4b0e0144516 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -426,6 +426,29 @@ config RISCV_ISA_V
 
 	  If you don't know what to do here, say Y.
 
+config TOOLCHAIN_HAS_ZBB
+	bool
+	default y
+	depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zbb)
+	depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zbb)
+	depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
+	depends on AS_IS_GNU
+
+config RISCV_ISA_ZBB
+	bool "Zbb extension support for bit manipulation instructions"
+	depends on TOOLCHAIN_HAS_ZBB
+	depends on !XIP_KERNEL && MMU
+	default y
+	help
+	   Adds support to dynamically detect the presence of the ZBB
+	   extension (basic bit manipulation) and enable its usage.
+
+	   The Zbb extension provides instructions to accelerate a number
+	   of bit-specific operations (count bit population, sign extending,
+	   bitrotation, etc).
+
+	   If you don't know what to do here, say Y.
+
 config TOOLCHAIN_HAS_ZICBOM
 	bool
 	default y
diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index f413db6118e5..c8c69b49f0ad 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -59,6 +59,7 @@ enum riscv_isa_ext_id {
 	RISCV_ISA_EXT_SSTC,
 	RISCV_ISA_EXT_SVINVAL,
 	RISCV_ISA_EXT_SVPBMT,
+	RISCV_ISA_EXT_ZBB,
 	RISCV_ISA_EXT_ZICBOM,
 	RISCV_ISA_EXT_ZIHINTPAUSE,
 	RISCV_ISA_EXT_ID_MAX
diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
index 0bf1c7f663fc..420228e219f7 100644
--- a/arch/riscv/kernel/cpu.c
+++ b/arch/riscv/kernel/cpu.c
@@ -185,6 +185,7 @@ arch_initcall(riscv_cpuinfo_init);
  * New entries to this struct should follow the ordering rules described above.
  */
 static struct riscv_isa_ext_data isa_ext_arr[] = {
+	__RISCV_ISA_EXT_DATA(zbb, RISCV_ISA_EXT_ZBB),
 	__RISCV_ISA_EXT_DATA(zicbom, RISCV_ISA_EXT_ZICBOM),
 	__RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
 	__RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index cbd60e744c09..33938f91cbbf 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -234,6 +234,7 @@ printk("!!!! isa-string: %s\n\n\n", isa);
 				SET_ISA_EXT_MAP("sstc", RISCV_ISA_EXT_SSTC);
 				SET_ISA_EXT_MAP("svinval", RISCV_ISA_EXT_SVINVAL);
 				SET_ISA_EXT_MAP("svpbmt", RISCV_ISA_EXT_SVPBMT);
+				SET_ISA_EXT_MAP("zbb", RISCV_ISA_EXT_ZBB);
 				SET_ISA_EXT_MAP("zicbom", RISCV_ISA_EXT_ZICBOM);
 				SET_ISA_EXT_MAP("zihintpause", RISCV_ISA_EXT_ZIHINTPAUSE);
 			}
-- 
2.39.0