[PATCH v3 1/2] Documentation: fpga: dfl: add PCI Identification documentation

[matthew.gerlach@linux.intel.com]

From: Matthew Gerlach <matthew.gerlach@linux.intel.com>

Add documentation on identifying FPGA based PCI cards prompted
by discussion on the linux-fpga@vger.kernel.org mailing list.

Signed-off-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
---
v3: Add url to page tracking PCI ID information for DFL based cards.

v2: Introduced in v2.
---
 Documentation/fpga/dfl.rst | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/Documentation/fpga/dfl.rst b/Documentation/fpga/dfl.rst
index 15b670926084..5144775b860a 100644
--- a/Documentation/fpga/dfl.rst
+++ b/Documentation/fpga/dfl.rst
@@ -507,6 +507,27 @@ ids application.
 https://github.com/OPAE/dfl-feature-id
 
 
+PCI Device Identification
+================================
+Since FPGA based PCI cards can be reconfigured to a perform a completely
+new function at runtime, properly identifying such cards and binding the
+correct driver can be challenging. In many use cases, deployed FPGA based
+PCI cards are essentially static and the PCI Product ID and Vendor ID pair
+is sufficient to identify the card.  The DFL framework helps with the
+dynamic case of deployed FPGA cards changing at run time by providing
+more detailed information about card discoverable at runtime.
+
+At one level, the DFL on a PCI card describes the function of the card.
+However, the same DFL could be instantiated on different physical cards.
+Conversely, different DFLs could be instantiated on the same physical card.
+Practical management of a cloud containing a heterogeneous set of such cards
+requires a PCI level of card identification. While the PCI Product ID and
+Vendor ID may be sufficient to bind the dfl-pci driver, it is expected
+that FPGA PCI cards would advertise suitable Subsystem ID and Subsystem
+Vendor ID values. Further PCI Product, Vendor, and Subsystem id tracking
+can be found at https://github.com/OPAE/dfl-feature-id/blob/main/dfl-pci-ids.rst.
+
+
 Location of DFLs on a PCI Device
 ================================
 The original method for finding a DFL on a PCI device assumed the start of the
-- 
2.25.1