mpc8xxx PCIe hotplug needs fixing, some clues ..

[Joakim Tjernlund]

Kumar Gala <galak at kernel.crashing.org> wrote on 2012/07/20 20:53:10:
>
>
> On Jul 20, 2012, at 2:17 AM, Joakim Tjernlund wrote:
>
> >
> > Hi Guys
> >
> > I see that you have been hacking Freescale PCI before so I send this to you(and the list)
> >
> > We are using PCIe(as RC) on P2010(basically a mpc85xx) and have PCI device that
> > started from user space (needs advance clock conf) so when linux boots there is
> > no device at all.
> > Trying to "hotplug" the device after it is enabled fails, no amount of recan/remove using
> > either fake or real hotplug makes a difference.
> >
> > I found the cause eventually but I can't fix it properly as I known almost nothing about PCI.
> > Cause:
> > indirect_pci.c:indirect_read_config() tests for if (hose->indirect_type & PPC_INDIRECT_TYPE_NO_PCIE_LINK)
> > and returns  PCIBIOS_DEVICE_NOT_FOUND
> >
> > PPC_INDIRECT_TYPE_NO_PCIE_LINK get set by fsl_pci.c (look for fsl_pcie_check_link) but is never cleared.
> > Clearing it as appropriate makes a small difference. If you
> > remove the RC and do a few of rescan's then the device appears.
> >
> > Hacking some more, like so:
> >
> > int fsl_pcie_check_link(struct pci_controller *hose)
> > {
> >    u32 val;
> >
> >    early_read_config_dword(hose, 0, 0, PCIE_LTSSM, &val);
> >    hose->indirect_type |= PPC_INDIRECT_TYPE_NO_PCIE_LINK;
> >    if (val < PCIE_LTSSM_L0)
> >       return 1;
> >    hose->indirect_type &= ~PPC_INDIRECT_TYPE_NO_PCIE_LINK;
> >    return 0;
> > }
> > and then using it carefully(it is easy to make linux hang) in indirect_read_config():
> > indirect_read_config(struct pci_bus *bus, unsigned int devfn, int offset,
> >            int len, u32 *val)
> > {
> >    struct pci_controller *hose = pci_bus_to_host(bus);
> >    volatile void __iomem *cfg_data;
> >    u8 cfg_type = 0;
> >    u32 bus_no, reg;
> >
> >    if (hose->indirect_type & PPC_INDIRECT_TYPE_NO_PCIE_LINK) {
> >       if (bus->number != hose->first_busno ||
> >           devfn != 0) {
> >          fsl_pcie_check_link(hose);
> >          return PCIBIOS_DEVICE_NOT_FOUND;
> >       }
> >    }
> >
> > Now it works, just one rescan and the device appears!
> > This is a hack, I don't known what other trouble it can cause, I hope you can
> > sort this out.
>
> How are you forcing the re-scan?  We can see if we can add a re-check of the link state in that flow somewhere.

echo 1 > /sys/bus/pci/rescan

Why is that check important? Seems like some very ppc specific workaround for something.

>
> Can you do a dump_stack() or something to get a call chain?

here?
indirect_read_config(struct pci_bus *bus, unsigned int devfn, int offset,
		     int len, u32 *val)
{
	struct pci_controller *hose = pci_bus_to_host(bus);
	volatile void __iomem *cfg_data;
	u8 cfg_type = 0;
	u32 bus_no, reg;
	static int first_dump;

	if (!first_dump) {
		dump_stack();
		first_dump = 1;
	}
...

I am not at work and and my board needs a reset button press to recover :(
Furthermore, my vacation starts next week, not sure I can get it fixed soon enough

 Jocke