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iMX6 PCIe MSI issues

Question asked by Robert Hancock on Nov 23, 2018

I am working with a custom FPGA PCI Express endpoint connected to an iMX6D, running the mainline 4.19.2 kernel. It seems happy using INTx interrupts but when trying to enable MSI the device driver is not receiving any interrupts.


From some register poking I have figured out:
-the MSI address set on the PCIe device is correctly set in the iMX MSI controller's MSI Controller Address register (0x1ffc820)
-the interrupt vectors are enabled in the MSI controller's Interrupt Enable register (0x1ffc828)
-the interrupt vectors are not masked in the MSI controller's Interrupt Mask register (0x1ffc82c)
-The MSI controller's Interrupt Status register (0x1ffc830) shows that the requested interrupt vectors are pending
-In the ARM GIC, vector 152 (for msi_ctrl_int) is enabled in the IS enable register (0x00a01110), but not set in the IS pending (0x00a01210) or IS active (0x00a01310) registers
-Vector 152 is not masked in the GPC interrupt mask (0x00a01310)
-Vector 152 is not active in the GPC interrupt status (0x00a01310)


So it appears the MSI controller is receiving and recognizing the MSI from the device, but the interrupt is not making it into the GIC for some reason. If I manually set vector 152 to pending in the GIC, the dw_handle_msi_irq handler in pci-designware-host.c does get called along with the interrupt handler(s) for the PCIe device, so it appears the chain from that point on is working:


# devmem 0x00a01210 32 0x1000000


I found someone else reporting this in 2014 with an unknown kernel version on the forums here, but with no resolution listed there:


Any ideas on what may be going wrong?