During baremetal host provisioning via ACM 2.14 / Metal3 on Cisco hardware, the ironic-conductor (sushy) fails to set the boot mode. The Redfish API returns a 400 Bad Request because the property "BootSourceOverrideMode" is either read-only or unsupported by the Cisco CIMC Redfish implementation.

Even after manually setting the hardware to UEFI and Secure Boot, Ironic attempts to patch the "BootSourceOverrideMode" to "UEFI", resulting in a fatal error that prevents the host from booting the discovery ISO.

Log snippet: 2026-02-03 07:08:13.542 1 ERROR ironic.drivers.modules.redfish.management [None req-f5103489-5928-4fce-9975-360e1dede01d] Setting boot mode to uefi failed for node bec24335-d444-4460-9d62-652897ca16c9. Error: HTTP PATCH https://<BMC_IP>/redfish/v1/Systems/WZP29020ZJN returned code 400. Base.1.13.0.GeneralError: Following properties in the request body cannot be updated because they are either read only, unknown or unsupported : "BootSourceOverrideMode" 

 OCP Hub: 4.18.14 ACM: 2.14 Hardware: Cisco CIMC 

 Always reproducible on this specific Cisco hardware/firmware combination when using the Redfish driver. 

Define a BareMetalHost (BMH) with bootMode: UEFI.

Attempt to provision the host using ZTP/ACM 2.14.

Observe the metal3-ironic pod logs during the management/provisioning phase. 

 Ironic attempts to send a PATCH request with {'Boot': {'BootSourceOverrideMode': 'UEFI'}}. The BMC rejects this with a 400 GeneralError, causing Ironic to fail the operation and stop the provisioning flow. 

 Ironic/Sushy should verify if "BootSourceOverrideMode" is a supported/writable property before attempting a PATCH. If the host is already in the desired boot mode (manually configured), the failure to PATCH should not be fatal, or the driver should use an alternative method compatible with Cisco Redfish. 

Manual verification via curl shows that UEFI is enabled on the host, but the "BootSourceOverrideMode" parameter is missing from the Redfish tree or marked as non-updatable.

Must-gather attached to the support case.