MIPS: smp-cps: prevent multi-core SMP with unsuitable CCA

If the user or bootloader sets the CCA to a value which is not suited
for multi-core SMP (ie. anything non-coherent) then limit the system to
using only a single core and warn the user.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>

1 files changed, 28 insertions, 2 deletions

diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
index 3c30891fc789..e2f78b34ff93 100644
--- a/arch/mips/kernel/smp-cps.c
+++ b/arch/mips/kernel/smp-cps.c
@@ -88,11 +88,38 @@ static void __init cps_smp_setup(void)
 
 static void __init cps_prepare_cpus(unsigned int max_cpus)
 {
-        unsigned ncores, core_vpes, c;
+        unsigned ncores, core_vpes, c, cca;
+        bool cca_unsuitable;
         u32 *entry_code;
 
         mips_mt_set_cpuoptions();
 
+        /* Detect whether the CCA is unsuited to multi-core SMP */
+        cca = read_c0_config() & CONF_CM_CMASK;
+        switch (cca) {
+        case 0x4: /* CWBE */
+        case 0x5: /* CWB */
+                /* The CCA is coherent, multi-core is fine */
+                cca_unsuitable = false;
+                break;
+
+        default:
+                /* CCA is not coherent, multi-core is not usable */
+                cca_unsuitable = true;
+        }
+
+        /* Warn the user if the CCA prevents multi-core */
+        ncores = mips_cm_numcores();
+        if (cca_unsuitable && ncores > 1) {
+                pr_warn("Using only one core due to unsuitable CCA 0x%x\n",
+                        cca);
+
+                for_each_present_cpu(c) {
+                        if (cpu_data[c].core)
+                                set_cpu_present(c, false);
+                }
+        }
+
         /* Patch the start of mips_cps_core_entry to provide the CM base */
         entry_code = (u32 *)&mips_cps_core_entry;
         UASM_i_LA(&entry_code, 3, (long)mips_cm_base);
@@ -100,7 +127,6 @@ static void __init cps_prepare_cpus(unsigned int max_cpus)
                             (void *)entry_code - (void *)&mips_cps_core_entry);
 
         /* Allocate core boot configuration structs */
-        ncores = mips_cm_numcores();
         mips_cps_core_bootcfg = kcalloc(ncores, sizeof(*mips_cps_core_bootcfg),
                                         GFP_KERNEL);
         if (!mips_cps_core_bootcfg) {