| 1 | Arm Server Base System Architecture Reference board (``sbsa-ref``) |
| 2 | ================================================================== |
| 3 | |
| 4 | The ``sbsa-ref`` board intends to look like real hardware (while the ``virt`` |
| 5 | board is a generic board platform that doesn't match any real hardware). |
| 6 | |
| 7 | The hardware part is defined by two specifications: |
| 8 | |
| 9 | - `Base System Architecture <https://developer.arm.com/documentation/den0094/>`__ (BSA) |
| 10 | - `Server Base System Architecture <https://developer.arm.com/documentation/den0029/>`__ (SBSA) |
| 11 | |
| 12 | The `Arm Base Boot Requirements <https://developer.arm.com/documentation/den0044/>`__ (BBR) |
| 13 | specification defines how the firmware reports that to any operating system. |
| 14 | |
| 15 | It is intended to be a machine for developing firmware and testing |
| 16 | standards compliance with operating systems. |
| 17 | |
| 18 | Supported devices |
| 19 | """"""""""""""""" |
| 20 | |
| 21 | The ``sbsa-ref`` board supports: |
| 22 | |
| 23 | - A configurable number of AArch64 CPUs |
| 24 | - GIC version 3 |
| 25 | - System bus AHCI controller |
| 26 | - System bus XHCI controller |
| 27 | - CDROM and hard disc on AHCI bus |
| 28 | - E1000E ethernet card on PCIe bus |
| 29 | - Bochs display adapter on PCIe bus |
| 30 | - A generic SBSA watchdog device |
| 31 | |
| 32 | |
| 33 | Board to firmware interface |
| 34 | """"""""""""""""""""""""""" |
| 35 | |
| 36 | ``sbsa-ref`` is a static system that reports a very minimal devicetree to the |
| 37 | firmware for non-discoverable information about system components. This |
| 38 | includes both internal hardware and parts affected by the qemu command line |
| 39 | (i.e. CPUs and memory). As a result it must have a firmware specifically built |
| 40 | to expect a certain hardware layout (as you would in a real machine). |
| 41 | |
| 42 | Note |
| 43 | '''' |
| 44 | |
| 45 | QEMU provides the guest EL3 firmware with minimal information about hardware |
| 46 | platform using minimalistic devicetree. This is not a Linux devicetree. It is |
| 47 | not even a firmware devicetree. |
| 48 | |
| 49 | It is information passed from QEMU to describe the information a hardware |
| 50 | platform would have other mechanisms to discover at runtime, that are affected |
| 51 | by the QEMU command line. |
| 52 | |
| 53 | Ultimately this devicetree may be replaced by IPC calls to an emulated SCP. |
| 54 | |
| 55 | DeviceTree information |
| 56 | '''''''''''''''''''''' |
| 57 | |
| 58 | The devicetree reports: |
| 59 | |
| 60 | - CPUs |
| 61 | - memory |
| 62 | - platform version |
| 63 | - GIC addresses |
| 64 | - NUMA node id for CPUs and memory |
| 65 | - CPU topology information |
| 66 | |
| 67 | Platform version |
| 68 | '''''''''''''''' |
| 69 | |
| 70 | The platform version is only for informing platform firmware about |
| 71 | what kind of ``sbsa-ref`` board it is running on. It is neither |
| 72 | a QEMU versioned machine type nor a reflection of the level of the |
| 73 | SBSA/SystemReady SR support provided. |
| 74 | |
| 75 | The ``machine-version-major`` value is updated when changes breaking |
| 76 | fw compatibility are introduced. The ``machine-version-minor`` value |
| 77 | is updated when features are added that don't break fw compatibility. |
| 78 | |
| 79 | Platform version changes: |
| 80 | |
| 81 | 0.0 |
| 82 | Devicetree holds information about CPUs, memory and platform version. |
| 83 | |
| 84 | 0.1 |
| 85 | GIC information is present in devicetree. |
| 86 | |
| 87 | 0.2 |
| 88 | GIC ITS information is present in devicetree. |
| 89 | |
| 90 | 0.3 |
| 91 | The USB controller is an XHCI device, not EHCI. |
| 92 | |
| 93 | 0.4 |
| 94 | CPU topology information is present in devicetree. |