[PATCH v2 2/2] Documentation: fpga: dfl: Add description for DFL UIO support

[Xu Yilun <yilun.xu@intel.com>]

This patch adds description for UIO support for dfl devices on DFL
bus.

Signed-off-by: Xu Yilun <yilun.xu@intel.com>
---
v2: no doc in v1, add it for v2.
---
 Documentation/fpga/dfl.rst | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/Documentation/fpga/dfl.rst b/Documentation/fpga/dfl.rst
index 0404fe6..a15e81e 100644
--- a/Documentation/fpga/dfl.rst
+++ b/Documentation/fpga/dfl.rst
@@ -502,6 +502,29 @@ FME Partial Reconfiguration Sub Feature driver (see drivers/fpga/dfl-fme-pr.c)
 could be a reference.
 
 
+UIO support for DFL devices
+===========================
+The FPGA is open for users to be reprogramed with newly developed hardware
+components. They could instantiate a new private feature in the DFL, and then
+get a DFL device in their system. In some cases users may need a userspace
+driver for the DFL device:
+
+* Users may need to run some diagnostic test for their hardwares.
+* Some hardware is designed for specific purposes and does not fit into one of
+  the standard kernel subsystems.
+
+This requires the direct access to the MMIO space and interrupt handling in
+userspace. We implemented a dfl-uio-pdev module which exposes the UIO device
+interfaces. It adds the uio_pdrv_genirq platform device with the resources of
+the DFL device, and let the generic UIO platform device driver provide UIO
+support to userspace.
+
+The DFL UIO driver has a special matching algorithem. It will match any DFL
+device which could not be handled by other DFL drivers. In this way, it will
+not impact the functionality of the features which are already supported by the
+system.
+
+
 Open discussion
 ===============
 FME driver exports one ioctl (DFL_FPGA_FME_PORT_PR) for partial reconfiguration
-- 
2.7.4