Date:   Fri, 20 Jan 2023 09:36:44 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Huacai Chen <chenhuacai@...il.com>
Cc:     Huacai Chen <chenhuacai@...ngson.cn>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        linux-pci@...r.kernel.org, Jianmin Lv <lvjianmin@...ngson.cn>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 2/2] PCI: Add quirk for LS7A to avoid reboot failure

On Fri, Jan 20, 2023 at 09:31:43PM +0800, Huacai Chen wrote:
> On Thu, Jan 19, 2023 at 8:50 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
> > On Thu, Jan 19, 2023 at 08:25:20PM +0800, Huacai Chen wrote:
> > > Ping?
> >
> > I suggested another possible way to do this that wasn't so much of a
> > special case.  Did you explore that at all?
>
> That is a little difficult for me, but what is worse is that the root
> cause doesn't come from gpu or console drivers, but from the root
> port. That means: even if we can workaround the gpu issue in another
> way, there are still problems on other devices. Besides the graphics
> card, the most frequent problematic device is the sata controller
> connected on LS7A chipset, there are incomplete I/O accesses after the
> root port disabled and also cause reboot failure.

Yes, SATA sounds like another case where we want to use the device
after we call the driver's remove/shutdown method.  That's not
*worse*, it's just another case where we might have to mark devices
for special handling.

If we remove/shutdown *any* Root Port, not just LS7A, I think the idea
of assuming downstream devices can continue to work as usual is a
little suspect.  They might continue to work by accident today, but it
doesn't seem like a robust design.

> > I know there's no *existing* way to mark devices that we need to use
> > all the way through shutdown or reboot, but if it makes sense, there's
> > no reason we couldn't add one.  That has the potential of being more
> > generic, e.g., we could do it for all console devices, as opposed to
> > quirking a Root Port that just happens to be in the path to the
> > console.
> >
> > > On Sat, Jan 7, 2023 at 10:25 AM Huacai Chen <chenhuacai@...il.com> wrote:
> > > > On Fri, Jan 6, 2023 at 11:38 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
> > > > > 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@...ngson.cn>
> > > > > > ---
> > > > > >  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
> > > > > >

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