lib: Fix CPU capabilities detection function

On some platforms, misa may not be implemented. On such a platform,
reading misa will get 0. At this time, platform is required to
implement a non-standard function to detect the CPU's capabilities.
Therefore, this modification add interfaces for non-standard function.

The MXL field of misa is always at the highest two bits, whether it
is a 32-bit 64-bit or a 128-bit machine. Therefore, this modification
fixes the use of a fixed offset to detect the machine length.

Signed-off-by: Xiang Wang <merle@hardenedlinux.org>
Signed-off-by: Anup Patel <anup.patel@wdc.com>

lib/sbi/riscv_asm.c

@@ -10,6 +10,38 @@
 #include <sbi/riscv_asm.h>
 #include <sbi/riscv_encoding.h>
 #include <sbi/sbi_error.h>
+#include <sbi/sbi_platform.h>
+
+int misa_extension(char ext)
+{
+	unsigned long misa = csr_read(CSR_MISA);
+
+	if (misa)
+		return misa & (1 << (ext - 'A'));
+
+	return sbi_platform_misa_extension(sbi_platform_thishart_ptr(), ext);
+}
+
+int misa_xlen(void)
+{
+	long r;
+
+	if (csr_read(CSR_MISA) == 0)
+		return sbi_platform_misa_xlen(sbi_platform_thishart_ptr());
+
+	__asm__ __volatile__(
+		"csrr   t0, misa\n\t"
+		"slti   t1, t0, 0\n\t"
+		"slli   t1, t1, 1\n\t"
+		"slli   t0, t0, 1\n\t"
+		"slti   t0, t0, 0\n\t"
+		"add    %0, t0, t1"
+		: "=r"(r)
+		:
+		: "t0", "t1");
+
+	return r ? r : -1;
+}
 
 unsigned long csr_read_num(int csr_num)
 {