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>

include/sbi/riscv_asm.h

@@ -159,22 +159,18 @@ void csr_write_num(int csr_num, unsigned long val);
 		__asm__ __volatile__("wfi" ::: "memory"); \
 	} while (0)
 
-static inline int misa_extension(char ext)
-{
-	return csr_read(CSR_MISA) & (1 << (ext - 'A'));
-}
+/* Determine CPU extension, return non-zero support */
+int misa_extension(char ext);
 
-static inline int misa_xlen(void)
-{
-	return ((long)csr_read(CSR_MISA) < 0) ? 64 : 32;
-}
+/* Get MXL field of misa, return -1 on error */
+int misa_xlen(void);
 
 static inline void misa_string(char *out, unsigned int out_sz)
 {
-	unsigned long i, val = csr_read(CSR_MISA);
+	unsigned long i;
 
 	for (i = 0; i < 26; i++) {
-		if (val & (1 << i)) {
+		if (misa_extension('A' + i)) {
 			*out = 'A' + i;
 			out++;
 		}

include/sbi/sbi_platform.h

@@ -76,6 +76,16 @@ struct sbi_platform_operations {
 	/** Platform final initialization */
 	int (*final_init)(bool cold_boot);
 
+	/** For platforms that do not implement misa, non-standard
+	 * methods are needed to determine cpu extension.
+	 */
+	int (*misa_check_extension)(char ext);
+
+	/** For platforms that do not implement misa, non-standard
+	 * methods are needed to get MXL field of misa.
+	 */
+	int (*misa_get_xlen)(void);
+
 	/** Get number of PMP regions for given HART */
 	u32 (*pmp_region_count)(u32 hartid);
 	/**
@@ -291,6 +301,36 @@ static inline int sbi_platform_final_init(const struct sbi_platform *plat,
 	return 0;
 }
 
+/**
+ * Check CPU extension in MISA
+ *
+ * @param plat pointer to struct sbi_platform
+ * @param ext shorthand letter for CPU extensions
+ *
+ * @return zero for not-supported and non-zero for supported
+ */
+static inline int sbi_platform_misa_extension(const struct sbi_platform *plat,
+					      char ext)
+{
+	if (plat && sbi_platform_ops(plat)->misa_check_extension)
+		return sbi_platform_ops(plat)->misa_check_extension(ext);
+	return 0;
+}
+
+/**
+ * Get MXL field of MISA
+ *
+ * @param plat pointer to struct sbi_platform
+ *
+ * @return 1/2/3 on success and error code on failure
+ */
+static inline int sbi_platform_misa_xlen(const struct sbi_platform *plat)
+{
+	if (plat && sbi_platform_ops(plat)->misa_get_xlen)
+		return sbi_platform_ops(plat)->misa_get_xlen();
+	return -1;
+}
+
 /**
  * Get the number of PMP regions of a HART
  *

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)
 {

lib/sbi/sbi_init.c

@@ -30,10 +30,10 @@
 
 static void sbi_boot_prints(struct sbi_scratch *scratch, u32 hartid)
 {
+	int xlen;
 	char str[64];
 	const struct sbi_platform *plat = sbi_platform_ptr(scratch);
 
-	misa_string(str, sizeof(str));
 #ifdef OPENSBI_VERSION_GIT
 	sbi_printf("\nOpenSBI %s\n", OPENSBI_VERSION_GIT);
 #else
@@ -43,9 +43,18 @@ static void sbi_boot_prints(struct sbi_scratch *scratch, u32 hartid)
 
 	sbi_printf(BANNER);
 
+	/* Determine MISA XLEN and MISA string */
+	xlen = misa_xlen();
+	if (xlen < 1) {
+		sbi_printf("Error %d getting MISA XLEN\n", xlen);
+		sbi_hart_hang();
+	}
+	xlen = 16 * (1 << xlen);
+	misa_string(str, sizeof(str));
+
 	/* Platform details */
 	sbi_printf("Platform Name          : %s\n", sbi_platform_name(plat));
-	sbi_printf("Platform HART Features : RV%d%s\n", misa_xlen(), str);
+	sbi_printf("Platform HART Features : RV%d%s\n", xlen, str);
 	sbi_printf("Platform Max HARTs     : %d\n",
 		   sbi_platform_hart_count(plat));
 	sbi_printf("Current Hart           : %u\n", hartid);