Friday June 24, 2005

Device Driver Development: How to add interrupts in a driver

                    New DDI interrupt interfaces

• Support new interrupt types like Message Signaled interrupts - MSIs and MSI-Xs
• Support new features like get/set priority,  get/set device interrupt capability, get interrupt pending information, set/clear interrupt mask etc.
• Support new Bus technologies like PCI-Express
• Have a generic framework that can support  other new (and unknown) interrupts where possible
  
• Support for multiple interrupts by a single device/function
• Existing interfaces are antiquated and provide limited features.

New DDI Interrupt Data structures

• Interrupt handles
• Interrupt handler
• Priority for Normal and Soft interrupts

Interrupt handles

• The 'Normal Interrupts' shown above use this handle
• ddi_intr_handle_t
  

•  The 'Soft Interrupts' use this handle
• ddi_intr_soft_handle_t
  

Interrupt handler

The interrupt handler has been modified to take two arguments
 /*
 * Typedef for driver's interrupt handler
 */
 typedef int (ddi_intr_handler_t)(void *arg1, void *arg2);

Interrupt Priority

Normal interrupt priority should be within the two defines shown below:
 #define DDI_INTR_PRI_MIN 1
 #define DDI_INTR_PRI_MAX 12

 priority is a small integer range from DDI_INTR_PRI_MIN to DDI_INTR_PRI_MAX for most drivers
 and represents virtual priority. It can be used directly in lock initialization calls: mutex_init, rw_init, etc.

Soft interrupt priority should be within the two defines shown below:
 #define DDI_INTR_SOFTPRI_MIN 1
 #define DDI_INTR_SOFTPRI_MAX 9

 By default most drivers could use the default Soft priority which is defined as
 #define DDI_INTR_SOFTPRI_DEFAULT 1

Calls to mutex_int() should use DDI_INTR_PRI() macro
 #define DDI_INTR_PRI(pri) (void *)((uintptr_t)(pri))

How Legacy Interrupt Functions map to new interfaces

New Interrupt Interface Examples

• Changing soft interrupt priority
• Checking for pending interrupts
• Setting interrupt masks
• Clearing interrupt masks

Example: Using the ddi_inter_set_softint_pri() Function

/* Change the soft interrupt priority to 9 */ 
if (ddi_intr_set_softint_pri(mydev->mydev_softint_hdl, 9) !=
 DDI_SUCCESS) {
 cmn_err (CE_WARN, "ddi_intr_set_softint_pri failed");
}

Example: Using the ddi_intr_get_pending() Function

/* Check if an interrupt is pending */
if (ddi_intr_get_pending(mydevp->htable[0], &pending) != DDI_SUCCESS) {
 cmn_err(CE_WARN, "ddi_intr_get_pending() failed");
} else if (pending)
 cmn_err(CE_NOTE, "ddi_intr_get_pending(): Interrupt pending");

Example: Using the ddi_intr_set_mask() Function

/* Set interrupt masking to prevent device from receiving interrupts */ 
if ((ddi_intr_set_mask(mydevp->htable[0]) != DDI_SUCCESS))
 cmn_err(CE_WARN, "ddi_intr_set_mask() failed");

Example: Using the ddi_intr_clr_mask() Function

/* Clear interrupt masking. If successful device will start generating interrupts */
if (ddi_intr_clr_mask(mydevp->htable[0]) != DDI_SUCCESS)
 cmn_err(CE_WARN, "ddi_intr_clr_mask() failed");

Reference: