title: irq_to_desc function failing with IRQ number
body: <p>I am trying to install an IRQ handler for the IRQ line 43 as below:</p>
  
  <pre><code>ret2 = request_irq(irq_no, handle_interrupt, IRQF_SHARED, DEVICE_NAME, &amp;pdev-&gt;dev);
  </code></pre>
  
  <p>But I keep on getting rquest_irq failed with -22 which is INVALID input. After looking into the kernel code I could see the function request_threaded_irq() is returning with -EINVAL at the below point:</p>
  
  <pre><code>desc = irq_to_desc(irq);
  if (!desc) {
      printk(KERN_EMERG "%s:%d\n", __func__, __LINE__);
      return -EINVAL;
  }
  </code></pre>
  
  <p>Can any one please help me understanding what could be the reason for the irq_to_desc() function to return NULL? 
  I am using Kernel version 4.11 in a mips machine. </p>
  
  <p>Thanks. </p>