ECAM Mapping and Addressing

The ECAM (Enhanced Configuration Access Mechanism) space is typically defined in the Device Tree (.dts file) under the PCIe node using the reg property:

In the example above:

• ECAM Base Address: 0x0600_0000_00

• ECAM Size: 0x0100_0000 (16 MB)

The probe function xilinx_cpm_pcie_probe, located in the file pcie-xilinx-cpm.c within the Linux kernel source (linux-xlnx/drivers/pci/controller/pcie-xilinx-cpm.c), is responsible for handling ECAM address mapping.

During system initialization in the CED, the following warning appears in the boot log:

This message indicates the following:

• The desired PCIe bus range is [bus 00-ff], which corresponds to bus numbers 0 through 255.

• However, due to the ECAM size limitation, the bus range is adjusted to [bus 00-0f], meaning only buses 0 through 15 are supported.

• The ECAM memory region is defined as [mem 0x600000000-0x600ffffff], totaling 16 MB.

Note

• Memory required per bus: Each bus requires 2^bus_shift bytes of memory. - For bus_shift = 20, this equals 1 MB per bus.

• Maximum number of buses supported: - 16 MB / 1 MB = 16 → Buses 0 through 15 can be addressed.

The following log snippet shows a successful mapping message: