[PATCH 05/13] riscv: vector: Use vlenb from DT for thead

[Charlie Jenkins <charlie@rivosinc.com>]

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

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
---
 arch/riscv/include/asm/cpufeature.h |  2 ++
 arch/riscv/kernel/cpufeature.c      | 48 +++++++++++++++++++++++++++++++++++++
 arch/riscv/kernel/vector.c          | 12 +++++++++-
 3 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index b029ca72cebc..e0a3164c7a06 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 thead_vlenb_of;
+
 void riscv_user_isa_enable(void);
 
 #define _RISCV_ISA_EXT_DATA(_name, _id, _subset_exts, _subset_exts_size) {	\
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 2107c59575dd..0c01f33f2348 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -37,6 +37,8 @@ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
 /* Per-cpu ISA extensions. */
 struct riscv_isainfo hart_isa[NR_CPUS];
 
+u32 thead_vlenb_of;
+
 /**
  * riscv_isa_extension_base() - Get base extension word
  *
@@ -625,6 +627,46 @@ static void __init riscv_fill_vendor_ext_list(int cpu)
 	}
 }
 
+static int has_thead_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, "thead,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);
+	}
+
+	thead_vlenb_of = vlenb;
+	return 0;
+}
+
 static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
 {
 	unsigned int cpu;
@@ -689,6 +731,12 @@ static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
 		riscv_fill_vendor_ext_list(cpu);
 	}
 
+	if (riscv_isa_vendor_extension_available(THEAD_VENDOR_ID, XTHEADVECTOR) &&
+	    has_thead_homogeneous_vlenb() < 0) {
+		pr_warn("Unsupported heterogeneous vlenb detected, vector extension disabled.\n");
+		elf_hwcap &= ~COMPAT_HWCAP_ISA_V;
+	}
+
 	if (bitmap_empty(riscv_isa, RISCV_ISA_EXT_MAX))
 		return -ENOENT;
 
diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
index 6727d1d3b8f2..3ba2f2432483 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 thead,vlenb property was provided by the firmware, use that
+	 * instead of probing the CSRs.
+	 */
+	if (thead_vlenb_of) {
+		this_vsize = thead_vlenb_of * 32;
+		return 0;
+	}
+
 	riscv_v_enable();
 	this_vsize = csr_read(CSR_VLENB) * 32;
 	riscv_v_disable();

-- 
2.44.0