Propose a Redfish PCIe design
This is a proposal to support the Redfish PCIe resources on
OpenBMC by using a defined D-Bus interface where Redfish
can get the current PCIe hardware information to display.
Change-Id: Ia67021f1dca3516345e22bd68e308b5f4811e868
Signed-off-by: Jason M. Bills <jason.m.bills@linux.intel.com>
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+# Redfish PCIe Resources
+
+Author:
+ Jason Bills, jmbills
+
+Primary assignee:
+ Jason Bills
+
+Other contributors:
+ Ed Tanous
+
+Created:
+ April 3, 2019
+
+## Problem Description
+Redfish has resources that describe PCIe devices and functions available
+on a system. It would be useful to provide these resources to users
+out-of-band over Redfish from OpenBMC.
+
+## Background and References
+The Redfish PCIe resources are here:
+
+[PCIeSlots](https://redfish.dmtf.org/schemas/PCIeSlots_v1.xml)
+
+[PCIeDevice](https://redfish.dmtf.org/schemas/PCIeDevice_v1.xml)
+
+[PCIeFunction](https://redfish.dmtf.org/schemas/PCIeFunction_v1.xml)
+
+## Requirements
+This feature is intended to meet the Redfish requirements for the PCIe
+resources above to provide useful system configuration information to system
+administrators and operators.
+
+## Proposed Design
+The proposed implementation will follow the standard D-Bus producer-consumer
+model used in OpenBMC. The producer will provide the required PCIe values read
+from hardware. The consumer will retrieve and parse the D-Bus data to provide
+the Redfish PCIe resources.
+
+The proposed D-Bus interface can be found here:
+https://gerrit.openbmc-project.xyz/c/openbmc/phosphor-dbus-interfaces/+/19768
+
+The proposed producer will be a new D-Bus daemon that will be responsible for
+gathering and caching PCIe hardware data and maintaining the D-Bus interfaces
+and properties. The actual hardware mechanism that is used to gather the PCIe
+hardware data will vary.
+
+For example, on systems that the BMC has access to the host PCI configuration
+space, it can directly read the required registers. On systems without access
+to the host PCI configuration space, an entity such as the BIOS or OS can
+gather the required data and send it to the PCIe daemon through IPMI, etc.
+
+When reading hardware directly, the PCIe daemon must be aware of power state
+changes and any BIOS timing requirements, so it can check for hardware
+changes, update its cache, and make the necessary changes to the D-Bus
+properties. This will allow a user to retrieve the latest PCIe resource data
+as of the last system boot even if it is powered off.
+
+bmcweb will be the consumer. It will be responsible for retrieving the Redfish
+PCIe resource data from the D-Bus properties and providing it to the user.
+
+## Alternatives Considered
+None.
+
+## Impacts
+Possible performance impact on the hardware-scanning and D-Bus updates.
+The piece that implements hardware scanning should use mechanisms,
+such as caching of the hardware configuration, to minimize the scanning time
+and updates to D-Bus properties.
+
+## Testing
+This can be tested using the Redfish Service Validator.