RISC-V: only iterate over possible CPUs in ISA string parser

During boot we call riscv_of_processor_hartid() for each hart that we
add to the possible cpus list. Repeating the call again here is not
required, if we iterate over the list of possible CPUs, rather than the
list of all CPUs.

The call to of_property_read_string() for "riscv,isa" cannot fail
either, as it has previously succeeded in riscv_of_processor_hartid(),
but leaving in the error checking makes the operation of the loop more
obvious & provides leeway for future refactoring of
riscv_of_processor_hartid().

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Co-developed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://lore.kernel.org/r/20230515054928.2079268-14-sunilvl@ventanamicro.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/kernel/cpufeature.c

@@ -12,6 +12,7 @@
 #include <linux/memory.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/of_device.h>
 #include <asm/alternative.h>
 #include <asm/cacheflush.h>
 #include <asm/cpufeature.h>
@@ -99,7 +100,7 @@ void __init riscv_fill_hwcap(void)
 	char print_str[NUM_ALPHA_EXTS + 1];
 	int i, j, rc;
 	unsigned long isa2hwcap[26] = {0};
-	unsigned long hartid;
+	unsigned int cpu;
 
 	isa2hwcap['i' - 'a'] = COMPAT_HWCAP_ISA_I;
 	isa2hwcap['m' - 'a'] = COMPAT_HWCAP_ISA_M;
@@ -112,16 +113,20 @@ void __init riscv_fill_hwcap(void)
 
 	bitmap_zero(riscv_isa, RISCV_ISA_EXT_MAX);
 
-	for_each_of_cpu_node(node) {
+	for_each_possible_cpu(cpu) {
 		unsigned long this_hwcap = 0;
 		DECLARE_BITMAP(this_isa, RISCV_ISA_EXT_MAX);
 		const char *temp;
 
-		rc = riscv_of_processor_hartid(node, &hartid);
-		if (rc < 0)
+		node = of_cpu_device_node_get(cpu);
+		if (!node) {
+			pr_warn("Unable to find cpu node\n");
 			continue;
+		}
 
-		if (of_property_read_string(node, "riscv,isa", &isa)) {
+		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;
 		}