On the i.MX6Quad (not QuadPlus), the PCIe link does not work after a suspend/resume cycle. Worse, the PCIe memory mapped I/O isn't accessible at all, so the system freezes when a PCIe driver tries to access its I/O space. The only way to get resume working again is to reset the PCIe link, similar to what is done on devices that support suspend/resume. Through trial and error, we found that something about the PCIe reference clock does not work as expected after a resume. We could not figure out if it is disabled (even though the registers still say it is enabled), or if it is somehow unstable or has some hiccups. With the workaround introduced in this patch series, we were able to fully resume a Compex WLE900VX (ath10k) miniPCIe Wifi module and an Intel AX200 M.2 Wifi module. If there is a better way or other ideas on how to fix this problem, please let us know. We are aware that resetting the link should not be necessary, but we could not find a better solution. More interestingly, even the SoCs that support suspend/resume according to the i.MX erratas seem to reset the link on resume in imx6_pcie_host_init, so we hope this might be a valid workaround. Stefan Eichenberger (3): PCI: imx6: Add a function to deassert the reset gpio PCI: imx6: move the wait for clock stabilization to enable ref clk PCI: imx6: reset link on resume drivers/pci/controller/dwc/pci-imx6.c | 69 +++++++++++++++++++++++---- 1 file changed, 59 insertions(+), 10 deletions(-) -- 2.43.0
