+/**
+ * sn_migrate - SN-specific task migration actions
+ * @task: Task being migrated to new CPU
+ *
+ * SN2 PIO writes from separate CPUs are not guaranteed to arrive in order.
+ * Context switching user threads which have memory-mapped MMIO may cause
+ * PIOs to issue from seperate CPUs, thus the PIO writes must be drained
+ * from the previous CPU's Shub before execution resumes on the new CPU.
+ */
+void sn_migrate(struct task_struct *task)
+{
+ pda_t *last_pda = pdacpu(task_thread_info(task)->last_cpu);
+ volatile unsigned long *adr = last_pda->pio_write_status_addr;
+ unsigned long val = last_pda->pio_write_status_val;
+
+ /* Drain PIO writes from old CPU's Shub */
+ while (unlikely((*adr & SH_PIO_WRITE_STATUS_PENDING_WRITE_COUNT_MASK)
+ != val))
+ cpu_relax();
+}
+