`requset_irq` vs `devm_request_irq`.

-. Same Feature: Support interrupt handling via kthread(request_threaded_irq).

-. Difference : `devm_*` additional support resource management for SoC based things.

-. How to use :  `request_irq` apply for custom PC driver.

                      `devm_request_irq` apply for SoC based platform driver 

                       for management platform_device's resource.

                      For example, Application Processor based platform.

-. `request_irq` (from http://lxr.free-electrons.com/source/kernel/irq/devres.c#L47)

128 request_irq(unsigned int irq, irq_handler_t handler, unsigned long flags,

             const char *name, void *dev)
 {
         return request_threaded_irq(irq, handler, NULL, flags, name, dev);
 }

-. `devm_request_irq` (from http://lxr.free-electrons.com/source/include/linux/interrupt.h#L128)

  int devm_request_threaded_irq(struct device *dev, unsigned int irq,
                                irq_handler_t handler, irq_handler_t thread_fn,
                                unsigned long irqflags, const char *devname,
                                void *dev_id)
  {
          struct irq_devres *dr;
          int rc;
  
          dr = devres_alloc(devm_irq_release, sizeof(struct irq_devres),
                            GFP_KERNEL);
          if (!dr)
                  return -ENOMEM;
  
          rc = request_threaded_irq(irq, handler, thread_fn, irqflags, devname,
                                    dev_id);
          if (rc) {
                  devres_free(dr);
                  return rc;
          }
  
          dr->irq = irq;
          dr->dev_id = dev_id;
          devres_add(dev, dr);
  
          return 0;
  }
  EXPORT_SYMBOL(devm_request_threaded_irq);