MIPS: disable MMID when not supported by the hardware

It is possible that MMID is supported at the CPU level, but its
integration in a SoC prevents its usage. For instance, if the
System-level Interconnect (also known as Network on Chip) does not
support global invalidation, then the MMID feature is not usable. The
current implementation of MMID relies on the GINV* instructions.

This patch allows the disabling of MMID based on a device tree
property, as this issue cannot be detected at runtime.

MMID is set up very early during the boot process, even before device
tree data can be accessed. Therefore, when we determine whether MMID
needs to be disabled, some MMID setup has already been performed for
the boot CPU. Consequently, we must revert the MMID setup on the first
CPU before disabling the feature for the subsequent CPUs that will be
initialized later.

Signed-off-by: Gregory CLEMENT <[e-mail]>
Signed-off-by: Thomas Bogendoerfer <[e-mail]>

arch/mips/include/asm/cpu-info.h

···
 
 extern void cpu_probe(void);
 extern void cpu_report(void);
+extern void cpu_disable_mmid(void);
 
 extern const char *__cpu_name[];
 #define cpu_name_string()	__cpu_name[raw_smp_processor_id()]

arch/mips/kernel/cpu-probe.c

···
  */
 #include <linux/init.h>
 #include <linux/kernel.h>
+#include <linux/mmu_context.h>
 #include <linux/ptrace.h>
 #include <linux/smp.h>
 #include <linux/stddef.h>
···
 /* Hardware capabilities */
 unsigned int elf_hwcap __read_mostly;
 EXPORT_SYMBOL_GPL(elf_hwcap);
+
+static bool mmid_disabled_quirk;
 
 static inline unsigned long cpu_get_msa_id(void)
 {
···
 	config5 &= ~(MIPS_CONF5_UFR | MIPS_CONF5_UFE);
 
 	if (cpu_has_mips_r6) {
-		if (!__builtin_constant_p(cpu_has_mmid) || cpu_has_mmid)
+		if (!mmid_disabled_quirk && (!__builtin_constant_p(cpu_has_mmid) || cpu_has_mmid))
 			config5 |= MIPS_CONF5_MI;
 		else
 			config5 &= ~MIPS_CONF5_MI;
···
 					max_mmid_width);
 				asid_mask = GENMASK(max_mmid_width - 1, 0);
 			}
-
 			set_cpu_asid_mask(c, asid_mask);
 		}
 	}
···
 
 	cpuinfo->globalnumber &= ~MIPS_GLOBALNUMBER_VP;
 	cpuinfo->globalnumber |= vpe << MIPS_GLOBALNUMBER_VP_SHF;
+}
+
+void cpu_disable_mmid(void)
+{
+	int i;
+	unsigned long asid_mask;
+	unsigned int cpu = smp_processor_id();
+	struct cpuinfo_mips *c = &current_cpu_data;
+	unsigned int config4 = read_c0_config4();
+	unsigned int config5 =  read_c0_config5();
+
+	/* Setup the initial ASID mask based on config4 */
+	asid_mask = MIPS_ENTRYHI_ASID;
+	if (config4 & MIPS_CONF4_AE)
+		asid_mask |= MIPS_ENTRYHI_ASIDX;
+	set_cpu_asid_mask(c, asid_mask);
+
+	/* Disable MMID in the C0 and update cpuinfo_mips accordingly */
+	config5 &= ~(MIPS_CONF5_UFR | MIPS_CONF5_UFE);
+	config5 &= ~MIPS_CONF5_MI;
+	write_c0_config5(config5);
+	/* Ensure the write to config5 above takes effect */
+	back_to_back_c0_hazard();
+	c->options &= ~MIPS_CPU_MMID;
+
+	/* Setup asid cache value cleared in per_cpu_trap_init() */
+	cpu_data[cpu].asid_cache = asid_first_version(cpu);
+
+	/* Reinit context for each CPU */
+	for_each_possible_cpu(i)
+		set_cpu_context(i, &init_mm, 0);
+
+	/* Ensure that now MMID will be seen as disable */
+	mmid_disabled_quirk = true;
+
+	pr_info("MMID support disabled due to hardware support issue\n");
 }

arch/mips/kernel/mips-cm.c

···
 		return;
 	pr_info("HCI (Hardware Cache Init for the L2 cache) in GCR_L2_RAM_CONFIG from the CM3 is broken");
 	mips_cm_is_l2_hci_broken = true;
+
+	/* Disable MMID only if it was configured */
+	if (cpu_has_mmid)
+		cpu_disable_mmid();
+
 	of_node_put(cm_node);
 }