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Date:   Sat, 27 Feb 2021 23:27:04 +0800
From:   Xu Yilun <>
Subject: [RESEND PATCH v11 2/2] Documentation: fpga: dfl: Add description for DFL UIO support

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

Signed-off-by: Xu Yilun <>
Reviewed-by: Tom Rix <>
Reviewed-by: Wu Hao <>
v2: no doc in v1, add it for v2.
v3: some documentation fixes.
v4: documentation change since the driver matching is changed.
v5: no change.
v6: improve the title of the userspace driver support section.
    some word improvement.
v7: rebased to next-20210119
v8: some doc fixes.
v9: some doc change since we switch to the driver in drivers/uio.
v10: no change.
v11: add description that interrupt support is not implemented yet.
 Documentation/fpga/dfl.rst | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/Documentation/fpga/dfl.rst b/Documentation/fpga/dfl.rst
index c41ac76..f3a1223 100644
--- a/Documentation/fpga/dfl.rst
+++ b/Documentation/fpga/dfl.rst
@@ -7,6 +7,7 @@ Authors:
 - Enno Luebbers <>
 - Xiao Guangrong <>
 - Wu Hao <>
+- Xu Yilun <>
 The Device Feature List (DFL) FPGA framework (and drivers according to
 this framework) hides the very details of low layer hardwares and provides
@@ -530,6 +531,31 @@ Being able to specify more than one DFL per BAR has been considered, but it
 was determined the use case did not provide value.  Specifying a single DFL
 per BAR simplifies the implementation and allows for extra error checking.
+Userspace driver support for DFL devices
+The purpose of an FPGA is to be reprogrammed with newly developed hardware
+components. New hardware can instantiate a new private feature in the DFL, and
+then present a DFL device in the system. In some cases users may need a
+userspace driver for the DFL device:
+* Users may need to run some diagnostic test for their hardware.
+* Users may prototype the kernel driver in user space.
+* Some hardware is designed for specific purposes and does not fit into one of
+  the standard kernel subsystems.
+This requires direct access to MMIO space and interrupt handling from
+userspace. The uio_dfl module exposes the UIO device interfaces for this
+Currently the uio_dfl driver only supports the Ether Group sub feature, which
+has no irq in hardware. So the interrupt handling is not added in this driver.
+UIO_DFL should be selected to enable the uio_dfl module driver. To support a
+new DFL feature via UIO direct access, its feature id should be added to the
+driver's id_table.
 Open discussion
 FME driver exports one ioctl (DFL_FPGA_FME_PORT_PR) for partial reconfiguration

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