linux-kernel - [PATCH 2/2] riscv: vector: Use vlenb from DT

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Message-Id: <20240515-add_vlenb_to_dt-v1-2-4ebd7cba0aa1@rivosinc.com>
Date: Wed, 15 May 2024 14:50:15 -0700
From: Charlie Jenkins <charlie@...osinc.com>
To: Conor Dooley <conor@...nel.org>, 
 Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>
Cc: Palmer Dabbelt <palmer@...ive.com>, linux-riscv@...ts.infradead.org, 
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Charlie Jenkins <charlie@...osinc.com>, 
 Conor Dooley <conor.dooley@...rochip.com>
Subject: [PATCH 2/2] riscv: vector: Use vlenb from DT

If vlenb is provided in the device tree, prefer that over reading the
vlenb csr.

Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
---
 arch/riscv/include/asm/cpufeature.h |  2 ++
 arch/riscv/kernel/cpufeature.c      | 47 +++++++++++++++++++++++++++++++++++++
 arch/riscv/kernel/vector.c          | 12 +++++++++-
 3 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index 347805446151..0c4f08577015 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -31,6 +31,8 @@ DECLARE_PER_CPU(struct riscv_cpuinfo, riscv_cpuinfo);
 /* Per-cpu ISA extensions. */
 extern struct riscv_isainfo hart_isa[NR_CPUS];
 
+extern u32 riscv_vlenb_of;
+
 void riscv_user_isa_enable(void);
 
 #if defined(CONFIG_RISCV_MISALIGNED)
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 3ed2359eae35..6c143ea9592b 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -35,6 +35,8 @@ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
 /* Per-cpu ISA extensions. */
 struct riscv_isainfo hart_isa[NR_CPUS];
 
+u32 riscv_vlenb_of;
+
 /**
  * riscv_isa_extension_base() - Get base extension word
  *
@@ -648,6 +650,46 @@ static int __init riscv_isa_fallback_setup(char *__unused)
 early_param("riscv_isa_fallback", riscv_isa_fallback_setup);
 #endif
 
+static int has_riscv_homogeneous_vlenb(void)
+{
+	int cpu;
+	u32 prev_vlenb = 0;
+	u32 vlenb;
+
+	/* Ignore vlenb if vector is not enabled in the kernel */
+	if (!IS_ENABLED(CONFIG_RISCV_ISA_V))
+		return 0;
+
+	for_each_possible_cpu(cpu) {
+		struct device_node *cpu_node;
+
+		cpu_node = of_cpu_device_node_get(cpu);
+		if (!cpu_node) {
+			pr_warn("Unable to find cpu node\n");
+			return -ENOENT;
+		}
+
+		if (of_property_read_u32(cpu_node, "riscv,vlenb", &vlenb)) {
+			of_node_put(cpu_node);
+
+			if (prev_vlenb)
+				return -ENOENT;
+			continue;
+		}
+
+		if (prev_vlenb && vlenb != prev_vlenb) {
+			of_node_put(cpu_node);
+			return -ENOENT;
+		}
+
+		prev_vlenb = vlenb;
+		of_node_put(cpu_node);
+	}
+
+	riscv_vlenb_of = vlenb;
+	return 0;
+}
+
 void __init riscv_fill_hwcap(void)
 {
 	char print_str[NUM_ALPHA_EXTS + 1];
@@ -671,6 +713,11 @@ void __init riscv_fill_hwcap(void)
 			pr_info("Falling back to deprecated \"riscv,isa\"\n");
 			riscv_fill_hwcap_from_isa_string(isa2hwcap);
 		}
+
+		if (elf_hwcap & COMPAT_HWCAP_ISA_V && has_riscv_homogeneous_vlenb() < 0) {
+			pr_warn("Unsupported heterogeneous vlen detected, vector extension disabled.\n");
+			elf_hwcap &= ~COMPAT_HWCAP_ISA_V;
+		}
 	}
 
 	/*
diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
index 6727d1d3b8f2..e04586cdb7f0 100644
--- a/arch/riscv/kernel/vector.c
+++ b/arch/riscv/kernel/vector.c
@@ -33,7 +33,17 @@ int riscv_v_setup_vsize(void)
 {
 	unsigned long this_vsize;
 
-	/* There are 32 vector registers with vlenb length. */
+	/*
+	 * There are 32 vector registers with vlenb length.
+	 *
+	 * If the riscv,vlenb property was provided by the firmware, use that
+	 * instead of probing the CSRs.
+	 */
+	if (riscv_vlenb_of) {
+		this_vsize = riscv_vlenb_of * 32;
+		return 0;
+	}
+
 	riscv_v_enable();
 	this_vsize = csr_read(CSR_VLENB) * 32;
 	riscv_v_disable();

-- 
2.44.0