Documentation: fpga: dfl: add descriptions for interrupt related interfaces.

This patch adds introductions of interrupt related interfaces for FME
error reporting, port error reporting and AFU user interrupts features.
Signed-off-by: Luwei Kang <luwei.kang@intel.com>
Signed-off-by: Wu Hao <hao.wu@intel.com>
Signed-off-by: Xu Yilun <yilun.xu@intel.com>
Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Acked-by: Wu Hao <hao.wu@intel.com>
Signed-off-by: Moritz Fischer <mdf@kernel.org>

Documentation/fpga/dfl.rst

@@ -89,6 +89,8 @@ The following functions are exposed through ioctls:
 - Program bitstream (DFL_FPGA_FME_PORT_PR)
 - Assign port to PF (DFL_FPGA_FME_PORT_ASSIGN)
 - Release port from PF (DFL_FPGA_FME_PORT_RELEASE)
+- Get number of irqs of FME global error (DFL_FPGA_FME_ERR_GET_IRQ_NUM)
+- Set interrupt trigger for FME error (DFL_FPGA_FME_ERR_SET_IRQ)
 
 More functions are exposed through sysfs
 (/sys/class/fpga_region/regionX/dfl-fme.n/):
@@ -149,6 +151,10 @@ The following functions are exposed through ioctls:
 - Map DMA buffer (DFL_FPGA_PORT_DMA_MAP)
 - Unmap DMA buffer (DFL_FPGA_PORT_DMA_UNMAP)
 - Reset AFU (DFL_FPGA_PORT_RESET)
+- Get number of irqs of port error (DFL_FPGA_PORT_ERR_GET_IRQ_NUM)
+- Set interrupt trigger for port error (DFL_FPGA_PORT_ERR_SET_IRQ)
+- Get number of irqs of UINT (DFL_FPGA_PORT_UINT_GET_IRQ_NUM)
+- Set interrupt trigger for UINT (DFL_FPGA_PORT_UINT_SET_IRQ)
 
 DFL_FPGA_PORT_RESET:
   reset the FPGA Port and its AFU. Userspace can do Port
@@ -462,6 +468,19 @@ since they are system-wide counters on FPGA device.
 The current driver does not support sampling. So "perf record" is unsupported.
 
 
+Interrupt support
+=================
+Some FME and AFU private features are able to generate interrupts. As mentioned
+above, users could call ioctl (DFL_FPGA_*_GET_IRQ_NUM) to know whether or how
+many interrupts are supported for this private feature. Drivers also implement
+an eventfd based interrupt handling mechanism for users to get notified when
+interrupt happens. Users could set eventfds to driver via
+ioctl (DFL_FPGA_*_SET_IRQ), and then poll/select on these eventfds waiting for
+notification.
+In Current DFL, 3 sub features (Port error, FME global error and AFU interrupt)
+support interrupts.
+
+
 Add new FIUs support
 ====================
 It's possible that developers made some new function blocks (FIUs) under this