Re: [PATCH V13 5/6] PCI: Add quirk for LS7A to avoid reboot failure

[Huacai Chen <chenhuacai@gmail.com>]

Hi, Bjorn,

On Wed, Jun 1, 2022 at 7:35 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> On Sat, Apr 30, 2022 at 04:48:45PM +0800, Huacai Chen wrote:
> > Commit cc27b735ad3a75574a ("PCI/portdrv: Turn off PCIe services during
> > shutdown")
>
> Usual quoting style would be
>
>   cc27b735ad3a ("PCI/portdrv: Turn off PCIe services during shutdown")
>   causes poweroff/reboot ...
OK, thanks.

>
> > causes poweroff/reboot failure on systems with LS7A chipset.
> > We found that if we remove "pci_command &= ~PCI_COMMAND_MASTER;" in
> > do_pci_disable_device(), it can work well. The hardware engineer says
> > that the root cause is that CPU is still accessing PCIe devices while
> > poweroff/reboot, and if we disable the Bus Master Bit at this time, the
> > PCIe controller doesn't forward requests to downstream devices, and also
> > doesn't send TIMEOUT to CPU, which causes CPU wait forever (hardware
> > deadlock). This behavior is a PCIe protocol violation (Bus Master should
> > not be involved in CPU MMIO transactions), and it will be fixed in new
> > revisions of hardware (add timeout mechanism for CPU read request,
> > whether or not Bus Master bit is cleared).
>
> LS7A might have bugs in that clearing Bus Master Enable prevents the
> root port from forwarding Memory or I/O requests in the downstream
> direction.
>
> But this feels like a bit of a band-aid because we don't know exactly
> what those requests are.  If we're removing the Root Port, I assume we
> think we no longer need any devices *below* the Root Port.
>
> If that's not the case, e.g., if we still need to produce console
> output or save state to a device, we probably should not be removing
> the Root Port at all.
Do you mean it is better to skip the whole pcie_port_device_remove()
instead of just removing the "clear bus master" operation for the
buggy hardware?

Huacai
>
> > On some x86 platforms, radeon/amdgpu devices can cause similar problems
> > [1][2]. Once before I wanted to make a single patch to solve "all of
> > these problems" together, but it seems unreasonable because maybe they
> > are not exactly the same problem. So, this patch just add a quirk for
> > LS7A to avoid clearing Bus Master bit in pcie_port_device_remove(), and
> > leave other platforms as is.
> >
> > [1] https://bugs.freedesktop.org/show_bug.cgi?id=97980
> > [2] https://bugs.freedesktop.org/show_bug.cgi?id=98638
> >
> > Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
> > ---
> >  drivers/pci/controller/pci-loongson.c | 17 +++++++++++++++++
> >  drivers/pci/pcie/portdrv_core.c       |  6 +++++-
> >  include/linux/pci.h                   |  1 +
> >  3 files changed, 23 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controller/pci-loongson.c
> > index 83447264048a..49d8b8c24ffb 100644
> > --- a/drivers/pci/controller/pci-loongson.c
> > +++ b/drivers/pci/controller/pci-loongson.c
> > @@ -85,6 +85,23 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
> >  DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
> >                       DEV_PCIE_PORT_2, loongson_mrrs_quirk);
> >
> > +static void loongson_bmaster_quirk(struct pci_dev *pdev)
> > +{
> > +     /*
> > +      * Some Loongson PCIe ports will cause CPU deadlock if disable
> > +      * the Bus Master bit during poweroff/reboot.
> > +      */
> > +     struct pci_host_bridge *bridge = pci_find_host_bridge(pdev->bus);
> > +
> > +     bridge->no_dis_bmaster = 1;
> > +}
> > +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
> > +                     DEV_PCIE_PORT_0, loongson_bmaster_quirk);
> > +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
> > +                     DEV_PCIE_PORT_1, loongson_bmaster_quirk);
> > +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
> > +                     DEV_PCIE_PORT_2, loongson_bmaster_quirk);
> > +
> >  static struct loongson_pci *pci_bus_to_loongson_pci(struct pci_bus *bus)
> >  {
> >       struct pci_config_window *cfg;
> > diff --git a/drivers/pci/pcie/portdrv_core.c b/drivers/pci/pcie/portdrv_core.c
> > index 604feeb84ee4..23f41e31a6c6 100644
> > --- a/drivers/pci/pcie/portdrv_core.c
> > +++ b/drivers/pci/pcie/portdrv_core.c
> > @@ -491,9 +491,13 @@ EXPORT_SYMBOL_GPL(pcie_port_find_device);
> >   */
> >  void pcie_port_device_remove(struct pci_dev *dev)
> >  {
> > +     struct pci_host_bridge *bridge = pci_find_host_bridge(dev->bus);
> > +
> >       device_for_each_child(&dev->dev, NULL, remove_iter);
> >       pci_free_irq_vectors(dev);
> > -     pci_disable_device(dev);
> > +
> > +     if (!bridge->no_dis_bmaster)
> > +             pci_disable_device(dev);
> >  }
> >
> >  /**
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index d146eb28e6da..c52d6486ff99 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -570,6 +570,7 @@ struct pci_host_bridge {
> >       unsigned int    ignore_reset_delay:1;   /* For entire hierarchy */
> >       unsigned int    no_ext_tags:1;          /* No Extended Tags */
> >       unsigned int    no_inc_mrrs:1;          /* No Increase MRRS */
> > +     unsigned int    no_dis_bmaster:1;       /* No Disable Bus Master */
> >       unsigned int    native_aer:1;           /* OS may use PCIe AER */
> >       unsigned int    native_pcie_hotplug:1;  /* OS may use PCIe hotplug */
> >       unsigned int    native_shpc_hotplug:1;  /* OS may use SHPC hotplug */
> > --
> > 2.27.0
> >