FROMLIST: PCI: dwc: Remove MSI/MSIX capability if iMSI-RX is used as …

[ziyuezhang-123]

…MSI controller

Some platforms may not support ITS (Interrupt Translation Service) and MBI (Message Based Interrupt), or there are not enough available empty SPI lines for MBI, in which case the msi-map and msi-parent property will not be provided in device tree node. For those cases, the DWC PCIe driver defaults to using the iMSI-RX module as MSI controller. However, due to DWC IP design, iMSI-RX cannot generate MSI interrupts for Root Ports even when MSI is properly configured and supported as iMSI-RX will only monitor and intercept incoming MSI TLPs from PCIe link, but the memory write generated by Root Port are internal system bus transactions instead of PCIe TLPs, so they are ignored.

This leads to interrupts such as PME, AER from the Root Port not received on the host and the users have to resort to workarounds such as passing "pcie_pme=nomsi" cmdline parameter.

To ensure reliable interrupt handling, remove MSI and MSI-X capabilities from Root Ports when using iMSI-RX as MSI controller, which is indicated by has_msi_ctrl == true. This forces a fallback to INTx interrupts, eliminating the need for manual kernel command line workarounds.

With this behavior:

• Platforms with ITS/MBI support use ITS/MBI MSI for interrupts from all components.
• Platforms without ITS/MBI support fall back to INTx for Root Ports and use iMSI-RX for other PCI devices.

Link: https://lore.kernel.org/all/20251109-remove_cap-v1-3-2208f46f4dc2@oss.qualcomm.com/