Re: [PATCH 08/11] PCI: dwc: Let glue drivers hide the Root Port MSI capabilities

Commit f5cd8a929c82 ("PCI: dwc: Remove MSI/MSIX capability for Root Port
if iMSI-RX is used as MSI controller") hides the Root Port MSI/MSI-X
capabilities when iMSI-RX is the MSI controller, as it cannot receive
the Root Port's own MSIs.

Some platforms cannot deliver them with an external MSI controller
either. The DesignWare core signals Root Port interrupts (AER, PME,
bandwidth, hotplug) as sideband signals on its SII interface and only
turns them into MSI writes with the optional SII2MSI feature. Otherwise
it is up to the vendor wrapper. R-Car Gen4 (DWC 5.20a) appears to lack
SII2MSI, and its APP block merely latches the signals into status
registers wired to platform IRQs, so an MSI targeted at the GIC ITS is
never sent.

Add a no_rp_msi flag so glue drivers can request the same INTx fallback
regardless of the MSI controller in use. It is the counterpart of
'keep_rp_msi_en' from commit 3a4e8302e72f ("PCI: imx6: Keep Root Port
MSI capability with iMSI-RX to work around hardware bug"), which keeps
precedence: that one is needed for endpoint MSIs to work at all, whereas
hiding the capability only moves the Root Port services to INTx. The
removal stays in dw_pcie_setup_rc(), which also runs after a Root Port
reset.

Signed-off-by: Koichiro Den <redacted>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260918032038.2216471-1-den@valinux.co.jp?part=8