MIPS: kdump: Add support

[ralf@linux-mips.org: Original patch by Maxim Uvarov <muvarov@gmail.com>
with plenty of further shining, polishing, debugging and testing by me.]

Signed-off-by: Maxim Uvarov <muvarov@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: kexec@lists.infradead.org
Cc: horms@verge.net.au
Patchwork: https://patchwork.linux-mips.org/patch/1025/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/crash.c

@@ -0,0 +1,71 @@
+#include <linux/kernel.h>
+#include <linux/smp.h>
+#include <linux/reboot.h>
+#include <linux/kexec.h>
+#include <linux/bootmem.h>
+#include <linux/crash_dump.h>
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/irq.h>
+#include <linux/types.h>
+#include <linux/sched.h>
+
+/* This keeps a track of which one is crashing cpu. */
+static int crashing_cpu = -1;
+static cpumask_t cpus_in_crash = CPU_MASK_NONE;
+
+#ifdef CONFIG_SMP
+static void crash_shutdown_secondary(void *ignore)
+{
+	struct pt_regs *regs;
+	int cpu = smp_processor_id();
+
+	regs = task_pt_regs(current);
+
+	if (!cpu_online(cpu))
+		return;
+
+	local_irq_disable();
+	if (!cpu_isset(cpu, cpus_in_crash))
+		crash_save_cpu(regs, cpu);
+	cpu_set(cpu, cpus_in_crash);
+
+	while (!atomic_read(&kexec_ready_to_reboot))
+		cpu_relax();
+	relocated_kexec_smp_wait(NULL);
+	/* NOTREACHED */
+}
+
+static void crash_kexec_prepare_cpus(void)
+{
+	unsigned int msecs;
+
+	unsigned int ncpus = num_online_cpus() - 1;/* Excluding the panic cpu */
+
+	dump_send_ipi(crash_shutdown_secondary);
+	smp_wmb();
+
+	/*
+	 * The crash CPU sends an IPI and wait for other CPUs to
+	 * respond. Delay of at least 10 seconds.
+	 */
+	pr_emerg("Sending IPI to other cpus...\n");
+	msecs = 10000;
+	while ((cpus_weight(cpus_in_crash) < ncpus) && (--msecs > 0)) {
+		cpu_relax();
+		mdelay(1);
+	}
+}
+
+#else /* !defined(CONFIG_SMP)  */
+static void crash_kexec_prepare_cpus(void) {}
+#endif /* !defined(CONFIG_SMP)  */
+
+void default_machine_crash_shutdown(struct pt_regs *regs)
+{
+	local_irq_disable();
+	crashing_cpu = smp_processor_id();
+	crash_save_cpu(regs, crashing_cpu);
+	crash_kexec_prepare_cpus();
+	cpu_set(crashing_cpu, cpus_in_crash);
+}