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docs: sbsa: update specs, add dt note
Hardware of sbsa-ref board is nowadays defined by both BSA and SBSA specifications. Then BBR defines firmware interface. Added note about DeviceTree data passed from QEMU to firmware. It is very minimal and provides only data we use in firmware. Added NUMA information to list of things reported by DeviceTree. Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org> Message-id: 20240328163851.1386176-1-marcin.juszkiewicz@linaro.org Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
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Arm Server Base System Architecture Reference board (``sbsa-ref``)
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Arm Server Base System Architecture Reference board (``sbsa-ref``)
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==================================================================
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==================================================================
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While the ``virt`` board is a generic board platform that doesn't match
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The ``sbsa-ref`` board intends to look like real hardware (while the ``virt``
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any real hardware the ``sbsa-ref`` board intends to look like real
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board is a generic board platform that doesn't match any real hardware).
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hardware. The `Server Base System Architecture
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<https://developer.arm.com/documentation/den0029/latest>`_ defines a
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The hardware part is defined by two specifications:
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minimum base line of hardware support and importantly how the firmware
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reports that to any operating system.
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- `Base System Architecture <https://developer.arm.com/documentation/den0094/>`__ (BSA)
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- `Server Base System Architecture <https://developer.arm.com/documentation/den0029/>`__ (SBSA)
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The `Arm Base Boot Requirements <https://developer.arm.com/documentation/den0044/>`__ (BBR)
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specification defines how the firmware reports that to any operating system.
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It is intended to be a machine for developing firmware and testing
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It is intended to be a machine for developing firmware and testing
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standards compliance with operating systems.
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standards compliance with operating systems.
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@ -35,16 +39,29 @@ includes both internal hardware and parts affected by the qemu command line
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(i.e. CPUs and memory). As a result it must have a firmware specifically built
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(i.e. CPUs and memory). As a result it must have a firmware specifically built
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to expect a certain hardware layout (as you would in a real machine).
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to expect a certain hardware layout (as you would in a real machine).
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Note
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''''
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QEMU provides the guest EL3 firmware with minimal information about hardware
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platform using minimalistic devicetree. This is not a Linux devicetree. It is
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not even a firmware devicetree.
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It is information passed from QEMU to describe the information a hardware
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platform would have other mechanisms to discover at runtime, that are affected
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by the QEMU command line.
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Ultimately this devicetree may be replaced by IPC calls to an emulated SCP.
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DeviceTree information
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DeviceTree information
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''''''''''''''''''''''
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''''''''''''''''''''''
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The devicetree provided by the board model to the firmware is not intended
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The devicetree reports:
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to be a complete compliant DT. It currently reports:
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- CPUs
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- CPUs
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- memory
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- memory
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- platform version
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- platform version
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- GIC addresses
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- GIC addresses
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- NUMA node id for CPUs and memory
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Platform version
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Platform version
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''''''''''''''''
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''''''''''''''''
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@ -70,4 +87,4 @@ Platform version changes:
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GIC ITS information is present in devicetree.
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GIC ITS information is present in devicetree.
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0.3
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0.3
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The USB controller is an XHCI device, not EHCI
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The USB controller is an XHCI device, not EHCI.
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