BCMA Interconnect

The bcma driver provides bhnd(4) support for devices using the ARM AMBA-based backplane architecture found in later Broadcom Home Networking Division's (HND) wireless chipsets and embedded systems.

BCMA uses AXI, bridged APB, and other ARM IP to support connectivity between the SoC/WiFi chipset IP cores.

Most of the IP cores used in siba(4) devices were adapted by Broadcom for compatibility with bcma, and common core device drivers can support both backplanes, generally transparently.

Device Enumeration

The ARM PL-368 "Device Management Plugin" system IP provides:

Wrapper cores that vend per-core device management register blocks.
An enumeration ROM providing the list of cores, their AXI master port identifiers, and any interconnect-mapped memory regions associated with their slave port(s) ("EROM table").

Documentation for the PL-368 is not publicly available; it has been described by Broadcom engineers as being ARM's PL-368 "Device Management Plugin" system IP as included with the PL3xx/AMBA Designer tooling licensed from ARM. The only public reference by ARM to its existence appears to be a reference to a proprietary/non-public "NIC-301 Interconnect Device Management (PL368)" errata document, included with ARM's "CoreLink Controllers and Peripherals" engineering errata.

The EROM table address can be found at offset 0xFC within the ChipCommon core's register block. The table itself is comprised of 32-bit type-tagged entries, organized into an array of variable-length core descriptor records.

The final core descriptor is followed by an EOF marker of 0x0000000F.

Each core descriptor record provides:

Hardware Identifiers:
- Designer (as a JEP106 Manufacturer Code)
- Part number
- Hardware revision
AXI master port IDs (unique across the bus) and port VID (unique per master). These are concatenated by the interconnect to form a unique master port ID.
Slave port descriptors, which define:
- The port type, which is one of:
  - Device (CSR register block)
  - Bridge (e.g. ARM's BP135 AXI2APB)
  - Wrapper (per-core DMP wrapper register block).
    - The memory regions mapped to this slave port by the interconnect.

Example BCM4331 EROM Table

  <Broadcom BCM4331 802.11a/b/g/n Wireless> mem 0xc0004000-0xc0007fff at device 4.0 on pci0
  core0: designer=Broadcom "ChipCommon" (entry=25004211 cid=800, rev=25, nmp=1, nsp=1, nwmp=1, nwsp=0)
    Master Port ID: 0.0
    Memory Regions:
      device0.0 at 0x18000000-0x18000fff
      mwrap0.0 at 0x18100000-0x18100fff
  core1: designer=Broadcom "802.11 MAC" (entry=1d004211 cid=812, rev=1d, nmp=1, nsp=1, nwmp=1, nwsp=0)
    Master Port ID: 1.0
    Memory Regions:
      device0.0 at 0x18001000-0x18001fff
      mwrap0.0 at 0x18101000-0x18101fff
  core2: designer=Broadcom "PCIe Bridge" (entry=13084411 cid=820, rev=13, nmp=1, nsp=2, nwmp=1, nwsp=1)
    Master Port ID: 2.0
    Memory Regions:
      device0.0 at 0x18002000-0x18002fff
      device1.0 at 0x08000000-0x0fffffff
      device1.1 at 0x8000000000000000-0xffffffffffffffff
      mwrap0.0 at 0x18102000-0x18102fff
      swrap1.0 at 0x18103000-0x18103fff
  core3: designer=ARM "AXI to APB Bridge" (entry=80201 cid=135, rev=0, nmp=0, nsp=1, nwmp=0, nwsp=1)
    Memory Regions:
      bridge0.0 at 0x18000000-0x18003fff
      swrap0.0 at 0x18104000-0x18104fff
  core4: designer=ARM "AXI to APB Bridge" (entry=80201 cid=135, rev=0, nmp=0, nsp=1, nwmp=0, nwsp=1)
    Memory Regions:
      bridge0.0 at 0x18100000-0x18108fff
      swrap0.0 at 0x18105000-0x18105fff
  core5: designer=ARM "OOB Interrupt Router" (entry=201 cid=367, rev=0, nmp=0, nsp=1, nwmp=0, nwsp=0)
    Memory Regions:
      device0.0 at 0x18106000-0x18106fff
  core6: designer=ARM "Enumeration ROM" (entry=201 cid=366, rev=0, nmp=0, nsp=1, nwmp=0, nwsp=0)
    Memory Regions:
      device0.0 at 0x18107000-0x18107fff
  core7: designer=ARM "AMBA AXI GPV" (entry=201 cid=301, rev=0, nmp=0, nsp=1, nwmp=0, nwsp=0)
    Memory Regions:
      device0.0 at 0x18003000-0x18003fff
  core8: designer=ARM "Default Core (Unused Address Ranges)" (entry=80201 cid=fff, rev=0, nmp=0, nsp=1, nwmp=0, nwsp=1)
    Memory Regions:
      device0.0 at 0x00000000-0x07ffffff
      device0.1 at 0x10000000-0x17ffffff
      device0.2 at 0x18004000-0x180fffff
      device0.3 at 0x18109000-0x7fffffffffffffff
      swrap0.0 at 0x18108000-0x18108fff