Alibaba's T-Head Yitan 710 SoC is built on Synopsys' widely deployed and
silicon-proven DesignWare Core PCIe controller which implements PMU for
performance and functional debugging to facilitate system maintenance.
Document it to provide guidance on how to use it.

Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
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 .../admin-guide/perf/dwc_pcie_pmu.rst         | 61 +++++++++++++++++++
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+======================================================================
+Synopsys DesignWare Cores (DWC) PCIe Performance Monitoring Unit (PMU)
+======================================================================
+
+DesignWare Cores (DWC) PCIe PMU
+===============================
+
+To facilitate collection of statistics, Synopsys DesignWare Cores PCIe
+controller provides the following two features:
+
+- Time Based Analysis (RX/TX data throughput and time spent in each
+  low-power LTSSM state)
+- Lane Event counters (Error and Non-Error for lanes)
+
+The PMU is not a PCIe Root Complex integrated End Point (RCiEP) device but
+only register counters provided by each PCIe Root Port.
+
+Time Based Analysis
+-------------------
+
+Using this feature you can obtain information regarding RX/TX data
+throughput and time spent in each low-power LTSSM state by the controller.
+
+The counters are 64-bit width and measure data in two categories,
+
+- percentage of time does the controller stay in LTSSM state in a
+  configurable duration. The measurement range of each Event in Group#0.
+- amount of data processed (Units of 16 bytes). The measurement range of
+  each Event in Group#1.
+
+Lane Event counters
+-------------------
+
+Using this feature you can obtain Error and Non-Error information in
+specific lane by the controller.
+
+The counters are 32-bit width and the measured event is select by:
+
+- Group i
+- Event j within the Group i
+- and Lank k
+
+Some of the event counters only exist for specific configurations.
+
+DesignWare Cores (DWC) PCIe PMU Driver
+=======================================
+
+This driver add PMU devices for each PCIe Root Port. And the PMU device is
+named based the BDF of Root Port. For example,
+
+    10:00.0 PCI bridge: Device 1ded:8000 (rev 01)
+
+the PMU device name for this Root Port is pcie_bdf_100000.
+
+Example usage of counting PCIe RX TLP data payload (Units of 16 bytes)::
+
+    $# perf stat -a -e pcie_bdf_200/Rx_PCIe_TLP_Data_Payload/