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Date:   Thu, 19 Jan 2023 06:50:00 -0600
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Huacai Chen <chenhuacai@gmail.com>
Cc:     Huacai Chen <chenhuacai@loongson.cn>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Rob Herring <robh@kernel.org>,
        Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kw@linux.com>,
        linux-pci@vger.kernel.org, Jianmin Lv <lvjianmin@loongson.cn>,
        Xuefeng Li <lixuefeng@loongson.cn>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH V2 2/2] PCI: Add quirk for LS7A to avoid reboot failure
Message-ID: <20230119125000.GA315545@bhelgaas>
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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?

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@gmail.com> wrote:
> >
> > On Fri, Jan 6, 2023 at 11:38 PM Bjorn Helgaas <helgaas@kernel.org> 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@loongson.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
> > > >