RISC-V: validate riscv,isa at boot, not during ISA string parsing

Since riscv_fill_hwcap() now only iterates over possible cpus, the
basic validation of whether riscv,isa contains "rv<width>" can be moved
to riscv_early_of_processor_hartid().

Further, "ima" support is required by the kernel, so reject any CPU not
fitting the bill.
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>
Link: https://lore.kernel.org/r/20230607-guts-blurry-67e711acf328@spudSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/kernel/cpu.c

@@ -65,10 +65,12 @@ int riscv_early_of_processor_hartid(struct device_node *node, unsigned long *har
 		pr_warn("CPU with hartid=%lu has no \"riscv,isa\" property\n", *hart);
 		return -ENODEV;
 	}
-	if (tolower(isa[0]) != 'r' || tolower(isa[1]) != 'v') {
-		pr_warn("CPU with hartid=%lu has an invalid ISA of \"%s\"\n", *hart, isa);
+
+	if (IS_ENABLED(CONFIG_32BIT) && strncasecmp(isa, "rv32ima", 7))
+		return -ENODEV;
+
+	if (IS_ENABLED(CONFIG_64BIT) && strncasecmp(isa, "rv64ima", 7))
 		return -ENODEV;
-	}
 
 	return 0;
 }

arch/riscv/kernel/cpufeature.c

@@ -148,12 +148,12 @@ void __init riscv_fill_hwcap(void)
 			}
 		}
 
-		if (IS_ENABLED(CONFIG_32BIT) && strncasecmp(isa, "rv32", 4))
-			continue;
-
-		if (IS_ENABLED(CONFIG_64BIT) && strncasecmp(isa, "rv64", 4))
-			continue;
-
+		/*
+		 * For all possible cpus, we have already validated in
+		 * the boot process that they at least contain "rv" and
+		 * whichever of "32"/"64" this kernel supports, and so this
+		 * section can be skipped.
+		 */
 		isa += 4;
 
 		bitmap_zero(this_isa, RISCV_ISA_EXT_MAX);