RISC-V: cpufeature: Add ACPI support in riscv_fill_hwcap()

On ACPI based systems, the information about the hart
like ISA is provided by the RISC-V Hart Capabilities Table (RHCT).
Enable filling up hwcap structure based on the information in RHCT.

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230515054928.2079268-15-sunilvl@ventanamicro.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/kernel/cpufeature.c

@@ -6,13 +6,15 @@
  * Copyright (C) 2017 SiFive
  */
 
+#include <linux/acpi.h>
 #include <linux/bitmap.h>
 #include <linux/ctype.h>
 #include <linux/log2.h>
 #include <linux/memory.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
+#include <asm/acpi.h>
 #include <asm/alternative.h>
 #include <asm/cacheflush.h>
 #include <asm/cpufeature.h>
@@ -100,6 +102,8 @@ void __init riscv_fill_hwcap(void)
 	char print_str[NUM_ALPHA_EXTS + 1];
 	int i, j, rc;
 	unsigned long isa2hwcap[26] = {0};
+	struct acpi_table_header *rhct;
+	acpi_status status;
 	unsigned int cpu;
 
 	isa2hwcap['i' - 'a'] = COMPAT_HWCAP_ISA_I;
@@ -113,22 +117,36 @@ void __init riscv_fill_hwcap(void)
 
 	bitmap_zero(riscv_isa, RISCV_ISA_EXT_MAX);
 
+	if (!acpi_disabled) {
+		status = acpi_get_table(ACPI_SIG_RHCT, 0, &rhct);
+		if (ACPI_FAILURE(status))
+			return;
+	}
+
 	for_each_possible_cpu(cpu) {
 		unsigned long this_hwcap = 0;
 		DECLARE_BITMAP(this_isa, RISCV_ISA_EXT_MAX);
 		const char *temp;
 
-		node = of_cpu_device_node_get(cpu);
-		if (!node) {
-			pr_warn("Unable to find cpu node\n");
-			continue;
-		}
+		if (acpi_disabled) {
+			node = of_cpu_device_node_get(cpu);
+			if (!node) {
+				pr_warn("Unable to find cpu node\n");
+				continue;
+			}
 
-		rc = of_property_read_string(node, "riscv,isa", &isa);
-		of_node_put(node);
-		if (rc) {
-			pr_warn("Unable to find \"riscv,isa\" devicetree entry\n");
-			continue;
+			rc = of_property_read_string(node, "riscv,isa", &isa);
+			of_node_put(node);
+			if (rc) {
+				pr_warn("Unable to find \"riscv,isa\" devicetree entry\n");
+				continue;
+			}
+		} else {
+			rc = acpi_get_riscv_isa(rhct, cpu, &isa);
+			if (rc < 0) {
+				pr_warn("Unable to get ISA for the hart - %d\n", cpu);
+				continue;
+			}
 		}
 
 		temp = isa;
@@ -265,6 +283,9 @@ void __init riscv_fill_hwcap(void)
 			bitmap_and(riscv_isa, riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
 	}
 
+	if (!acpi_disabled && rhct)
+		acpi_put_table((struct acpi_table_header *)rhct);
+
 	/* We don't support systems with F but without D, so mask those out
 	 * here. */
 	if ((elf_hwcap & COMPAT_HWCAP_ISA_F) && !(elf_hwcap & COMPAT_HWCAP_ISA_D)) {