Re: [PATCH V2 2/2] PCI: Add quirk for LS7A to avoid reboot failure

[Huacai Chen]

On Fri, Jan 6, 2023 at 11:38 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> [+cc Rafael, linux-pm, linux-kernel in case you have comments on
> whether devices should still be usable after .remove()/.shutdown()]
>
> On Fri, Jan 06, 2023 at 05:51:43PM +0800, Huacai Chen wrote:
> > After cc27b735ad3a7557 ("PCI/portdrv: Turn off PCIe services during
> > shutdown") we observe poweroff/reboot failures 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
> > does not send TIMEOUT to CPU, which causes CPU wait forever (hardware
> > deadlock).
> >
> > To be clear, the sequence is like this:
> >
> >   - CPU issues MMIO read to device below Root Port
> >
> >   - LS7A Root Port fails to forward transaction to secondary bus
> >     because of LS7A Bus Master defect
> >
> >   - CPU hangs waiting for response to MMIO read
> >
> > Then how is userspace able to use a device after the device is removed?
> >
> > To give more details, let's take the graphics driver (e.g. amdgpu) as
> > an example. The userspace programs call printf() to display "shutting
> > down xxx service" during shutdown/reboot, or the kernel calls printk()
> > to display something during shutdown/reboot. These can happen at any
> > time, even after we call pcie_port_device_remove() to disable the pcie
> > port on the graphic card.
> >
> > The call stack is: printk() --> call_console_drivers() --> con->write()
> > --> vt_console_print() --> fbcon_putcs()
> >
> > This scenario happens because userspace programs (or the kernel itself)
> > don't know whether a device is 'usable', they just use it, at any time.
>
> Thanks for this background.  So basically we want to call .remove() on
> a console device (or a bridge leading to it), but we expect it to keep
> working as usual afterwards?
>
> That seems a little weird.  Is that the design we want?  Maybe we
> should have a way to mark devices so we don't remove them during
> shutdown or reboot?
Sounds reasonable, but it seems no existing way can mark this.

Huacai
>
> > This hardware 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).
> >
> > 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 add a new function
> > pcie_portdrv_shutdown(), a slight modified copy of pcie_portdrv_remove()
> > dedicated for the shutdown path, and then add a quirk just for LS7A to
> > avoid clearing Bus Master bit in pcie_portdrv_shutdown(). Leave other
> > platforms behave as before.
> >
> > [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@xxxxxxxxxxx>
> > ---
> >  drivers/pci/controller/pci-loongson.c | 17 +++++++++++++++++
> >  drivers/pci/pcie/portdrv.c            | 21 +++++++++++++++++++--
> >  include/linux/pci.h                   |  1 +
> >  3 files changed, 37 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controller/pci-loongson.c
> > index 759ec211c17b..641308ba4126 100644
> > --- a/drivers/pci/controller/pci-loongson.c
> > +++ b/drivers/pci/controller/pci-loongson.c
> > @@ -93,6 +93,24 @@ 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 there is
> > +      * MMIO access to a downstream device when the root port 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 void loongson_pci_pin_quirk(struct pci_dev *pdev)
> >  {
> >       pdev->pin = 1 + (PCI_FUNC(pdev->devfn) & 3);
> > diff --git a/drivers/pci/pcie/portdrv.c b/drivers/pci/pcie/portdrv.c
> > index 2cc2e60bcb39..96f45c444422 100644
> > --- a/drivers/pci/pcie/portdrv.c
> > +++ b/drivers/pci/pcie/portdrv.c
> > @@ -501,7 +501,6 @@ static void pcie_port_device_remove(struct pci_dev *dev)
> >  {
> >       device_for_each_child(&dev->dev, NULL, remove_iter);
> >       pci_free_irq_vectors(dev);
> > -     pci_disable_device(dev);
> >  }
> >
> >  /**
> > @@ -727,6 +726,24 @@ static void pcie_portdrv_remove(struct pci_dev *dev)
> >       }
> >
> >       pcie_port_device_remove(dev);
> > +
> > +     pci_disable_device(dev);
> > +}
> > +
> > +static void pcie_portdrv_shutdown(struct pci_dev *dev)
> > +{
> > +     struct pci_host_bridge *bridge = pci_find_host_bridge(dev->bus);
> > +
> > +     if (pci_bridge_d3_possible(dev)) {
> > +             pm_runtime_forbid(&dev->dev);
> > +             pm_runtime_get_noresume(&dev->dev);
> > +             pm_runtime_dont_use_autosuspend(&dev->dev);
> > +     }
> > +
> > +     pcie_port_device_remove(dev);
> > +
> > +     if (!bridge->no_dis_bmaster)
> > +             pci_disable_device(dev);
> >  }
> >
> >  static pci_ers_result_t pcie_portdrv_error_detected(struct pci_dev *dev,
> > @@ -777,7 +794,7 @@ static struct pci_driver pcie_portdriver = {
> >
> >       .probe          = pcie_portdrv_probe,
> >       .remove         = pcie_portdrv_remove,
> > -     .shutdown       = pcie_portdrv_remove,
> > +     .shutdown       = pcie_portdrv_shutdown,
> >
> >       .err_handler    = &pcie_portdrv_err_handler,
> >
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index 3df2049ec4a8..a64dbcb89231 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -573,6 +573,7 @@ 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 */
> > --
> > 2.31.1
> >