riscv: vector: Use vlenb from DT for thead

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

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Tested-by: Yangyu Chen <cyy@cyyself.name>
Link: https://lore.kernel.org/r/20241113-xtheadvector-v11-5-236c22791ef9@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/Kconfig.vendor

@@ -26,6 +26,19 @@ config RISCV_ISA_VENDOR_EXT_THEAD
 	  extensions. Without this option enabled, T-Head vendor extensions will
 	  not be detected at boot and their presence not reported to userspace.
 
+	  If you don't know what to do here, say Y.
+
+config RISCV_ISA_XTHEADVECTOR
+	bool "xtheadvector extension support"
+	depends on RISCV_ISA_VENDOR_EXT_THEAD
+	depends on RISCV_ISA_V
+	depends on FPU
+	default y
+	help
+	  Say N here if you want to disable all xtheadvector related procedures
+	  in the kernel. This will disable vector for any T-Head board that
+	  contains xtheadvector rather than the standard vector.
+
 	  If you don't know what to do here, say Y.
 endmenu
 

arch/riscv/include/asm/cpufeature.h

@@ -34,6 +34,8 @@ 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 __init riscv_user_isa_enable(void);
 
 #define _RISCV_ISA_EXT_DATA(_name, _id, _subset_exts, _subset_exts_size, _validate) {	\

arch/riscv/include/asm/vendor_extensions/thead.h

@@ -13,4 +13,10 @@
 
 extern struct riscv_isa_vendor_ext_data_list riscv_isa_vendor_ext_list_thead;
 
+#ifdef CONFIG_RISCV_ISA_VENDOR_EXT_THEAD
+void disable_xtheadvector(void);
+#else
+static inline void disable_xtheadvector(void) { }
+#endif
+
 #endif

arch/riscv/kernel/cpufeature.c

@@ -39,6 +39,8 @@ 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
  *
@@ -779,6 +781,46 @@ 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 thead,vlenb property if xtheavector is not enabled in the kernel */
+	if (!IS_ENABLED(CONFIG_RISCV_ISA_XTHEADVECTOR))
+		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;
@@ -832,6 +874,12 @@ 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");
+		disable_xtheadvector();
+	}
+
 	if (bitmap_empty(riscv_isa, RISCV_ISA_EXT_MAX))
 		return -ENOENT;
 

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) {
+		riscv_v_vsize = thead_vlenb_of * 32;
+		return 0;
+	}
+
 	riscv_v_enable();
 	this_vsize = csr_read(CSR_VLENB) * 32;
 	riscv_v_disable();

arch/riscv/kernel/vendor_extensions/thead.c

@@ -5,6 +5,7 @@
 #include <asm/vendor_extensions/thead.h>
 
 #include <linux/array_size.h>
+#include <linux/cpumask.h>
 #include <linux/types.h>
 
 /* All T-Head vendor extensions supported in Linux */
@@ -16,3 +17,13 @@ struct riscv_isa_vendor_ext_data_list riscv_isa_vendor_ext_list_thead = {
 	.ext_data_count = ARRAY_SIZE(riscv_isa_vendor_ext_thead),
 	.ext_data = riscv_isa_vendor_ext_thead,
 };
+
+void disable_xtheadvector(void)
+{
+	int cpu;
+
+	for_each_possible_cpu(cpu)
+		clear_bit(RISCV_ISA_VENDOR_EXT_XTHEADVECTOR, riscv_isa_vendor_ext_list_thead.per_hart_isa_bitmap[cpu].isa);
+
+	clear_bit(RISCV_ISA_VENDOR_EXT_XTHEADVECTOR, riscv_isa_vendor_ext_list_thead.all_harts_isa_bitmap.isa);
+}