MIPS: CM: Fix mips_cm_max_vp_width for non-MT kernels on MT systems

When discovering the number of VPEs per core, smp_num_siblings will be
incorrect for kernels built without support for the MIPS MultiThreading
(MT) ASE running on systems which implement said ASE. This leads to
accesses to VPEs in secondary cores being performed incorrectly since
mips_cm_vp_id calculates the wrong ID to write to the local "other"
registers. Fix this by examining the number of VPEs in the core as
reported by the CM.

This patch presumes that the number of VPEs will be the same in each
core of the system. As this path only applies to systems with CM version
2.5 or lower, and this property is true of all such known systems, this
is likely to be fine but is described in a comment for good measure.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14338/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

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

@@ -458,10 +458,21 @@ static inline int mips_cm_revision(void)
 static inline unsigned int mips_cm_max_vp_width(void)
 {
 	extern int smp_num_siblings;
+	uint32_t cfg;
 
 	if (mips_cm_revision() >= CM_REV_CM3)
 		return read_gcr_sys_config2() & CM_GCR_SYS_CONFIG2_MAXVPW_MSK;
 
+	if (mips_cm_present()) {
+		/*
+		 * We presume that all cores in the system will have the same
+		 * number of VP(E)s, and if that ever changes then this will
+		 * need revisiting.
+		 */
+		cfg = read_gcr_cl_config() & CM_GCR_Cx_CONFIG_PVPE_MSK;
+		return (cfg >> CM_GCR_Cx_CONFIG_PVPE_SHF) + 1;
+	}
+
 	if (IS_ENABLED(CONFIG_SMP))
 		return smp_num_siblings;