MIPS: mips-cm: Implement mips_cm_revision

Provide a function to trivially return the version of the CM present in
the system, or 0 if no CM is present. The mips_cm_revision() will be
used later on to determine the CM register width, so it must not use
the regular CM accessors to read the revision register since that will
lead to build failures due to recursive inlines.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10655/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/mips-cm.h

@@ -189,6 +189,13 @@ BUILD_CM_Cx_R_(tcid_8_priority,	0x80)
 #define CM_GCR_REV_MINOR_SHF			0
 #define CM_GCR_REV_MINOR_MSK			(_ULCAST_(0xff) << 0)
 
+#define CM_ENCODE_REV(major, minor) \
+		(((major) << CM_GCR_REV_MAJOR_SHF) | \
+		 ((minor) << CM_GCR_REV_MINOR_SHF))
+
+#define CM_REV_CM2				CM_ENCODE_REV(6, 0)
+#define CM_REV_CM3				CM_ENCODE_REV(8, 0)
+
 /* GCR_ERROR_CAUSE register fields */
 #define CM_GCR_ERROR_CAUSE_ERRTYPE_SHF		27
 #define CM_GCR_ERROR_CAUSE_ERRTYPE_MSK		(_ULCAST_(0x1f) << 27)
@@ -324,4 +331,18 @@ static inline int mips_cm_l2sync(void)
 	return 0;
 }
 
+/**
+ * mips_cm_revision() - return CM revision
+ *
+ * Return: The revision of the CM, from GCR_REV, or 0 if no CM is present. The
+ * return value should be checked against the CM_REV_* macros.
+ */
+static inline int mips_cm_revision(void)
+{
+	if (!mips_cm_present())
+		return 0;
+
+	return read_gcr_rev();
+}
+
 #endif /* __MIPS_ASM_MIPS_CM_H__ */