Re: [PATCH v1 0/3] PCI: imx6: reset link after suspend/resume

[Stefan Eichenberger <eichest@gmail.com>]

Hi Frank,

On Tue, Aug 20, 2024 at 08:52:41AM +0200, Stefan Eichenberger wrote:
> On Mon, Aug 19, 2024 at 10:30:38AM -0400, Frank Li wrote:
> > On Mon, Aug 19, 2024 at 11:03:16AM +0200, Stefan Eichenberger wrote:
> > > 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
> > 
> > Thanks you for your patch, but it may have conflict with
> > https://lore.kernel.org/linux-pci/Zr4XG6r+HnbIlu8S@lizhi-Precision-Tower-5810/T/#t
> > 
> 
> Thanks a lot for the hint. I will have a look at the series and see if I
> can adapt my changes including your suggestions.

I did some more tests with your series applied. Everything works as
expected on an i.MX8M Plus. However, the i.MX6Quad PCIe link still does
not work after a resume. I could trace the issues back to the following
functions, besides that we could use the same suspend/resume function as
for the other i.MX SoCs.

In suspend the follwoing function is causing issues:
imx_pcie_stop_link(imx_pcie->pci);

In resume the following functions are causing issues:
imx_pcie->drvdata->init_phy(imx_pcie); // in imx_pcie_host_init
imx_pcie_start_link(imx_pcie->pci);

I think the second one makes sense because I could not stop the link I
should not start it again. But why is also the init_phy function
failing? Are they required to setup the link? 

The messages I get when the system resumes are:
[   50.176212] Enabling non-boot CPUs ...
[   50.194446] CPU1 is up
[   50.198087] CPU2 is up
[   50.201746] CPU3 is up
[   50.563710] imx6q-pcie 1ffc000.pcie: Read DBI address failed

After the last message the system hangs. It seems this happens because
the PCIe I/O mem is not accessible anymore.

Do you have an idea what could cause imx_pcie_stop_link to break the
link on resume? Without calling them the link is working fine after
resuming and the drivers can access the PCIe I/O mem.

Thanks,
Stefan