Re: [RFC PATCH v2] PCI/portdrv: Only disable Bus Master on kexec reboot and connected PCI devices

[Huacai Chen]

Hi, Tiezhu

> ------------------ Original ------------------
> From:  "Tiezhu Yang"<yangtiezhu@xxxxxxxxxxx>;
> Date:  Mon, Sep 14, 2020 04:29 AM
> To:  "Bjorn Helgaas"<bhelgaas@xxxxxxxxxx>;
> Cc:  "Konstantin Khlebnikov"<khlebnikov@xxxxxxxxxx>; "Khalid Aziz"<khalid.aziz@xxxxxxxxxx>; "Vivek Goyal"<vgoyal@xxxxxxxxxx>; "Lukas Wunner"<lukas@xxxxxxxxx>; "oohall"<oohall@xxxxxxxxx>; "rafael.j.wysocki"<rafael.j.wysocki@xxxxxxxxx>; "Xuefeng Li"<lixuefeng@xxxxxxxxxxx>; "Huacai Chen"<chenhc@xxxxxxxxxx>; "Jiaxun Yang"<jiaxun.yang@xxxxxxxxxxx>; "linux-pci"<linux-pci@xxxxxxxxxxxxxxx>; "linux-kernel"<linux-kernel@xxxxxxxxxxxxxxx>;
> Subject:  [RFC PATCH v2] PCI/portdrv: Only disable Bus Master on kexec reboot and connected PCI devices
>
>
>
> After commit 745be2e700cd ("PCIe: portdrv: call pci_disable_device
> during remove") and commit cc27b735ad3a ("PCI/portdrv: Turn off PCIe
> services during shutdown"), it also calls pci_disable_device() during
> shutdown, this leads to shutdown or reboot failure occasionally due to
> clear PCI_COMMAND_MASTER on the device in do_pci_disable_device().
>
> drivers/pci/pci.c
> static void do_pci_disable_device(struct pci_dev *dev)
> {
>         u16 pci_command;
>
>         pci_read_config_word(dev, PCI_COMMAND, &pci_command);
>         if (pci_command & PCI_COMMAND_MASTER) {
>                 pci_command &= ~PCI_COMMAND_MASTER;
>                 pci_write_config_word(dev, PCI_COMMAND, pci_command);
>         }
>
>         pcibios_disable_device(dev);
> }
>
> When remove "pci_command &= ~PCI_COMMAND_MASTER;", it can work well.
>
> As Oliver O'Halloran said, no need to call pci_disable_device() when
> actually shutting down, but we should call pci_disable_device() before
> handing over to the new kernel on kexec reboot, so we can do some
> condition checks which are similar with pci_device_shutdown(), this is
> done by commit 4fc9bbf98fd6 ("PCI: Disable Bus Master only on kexec
> reboot") and commit 6e0eda3c3898 ("PCI: Don't try to disable Bus Master
> on disconnected PCI devices").
>
> drivers/pci/pci-driver.c
> static void pci_device_shutdown(struct device *dev)
> {
> ...
>
>         /*
>          * If this is a kexec reboot, turn off Bus Master bit on the
>          * device to tell it to not continue to do DMA. Don't touch
>          * devices in D3cold or unknown states.
>          * If it is not a kexec reboot, firmware will hit the PCI
>          * devices with big hammer and stop their DMA any way.
>          */
>         if (kexec_in_progress && (pci_dev->current_state <= PCI_D3hot))
>                 pci_clear_master(pci_dev);
> }
Have you really tried kexec? Why do you think kexec can disable pci
device successfully while normal reboot/poweroff cannot?

Huacai
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> ---
>  drivers/pci/pcie/portdrv_core.c |  1 -
>  drivers/pci/pcie/portdrv_pci.c  | 25 ++++++++++++++++++++++++-
>  2 files changed, 24 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/pcie/portdrv_core.c b/drivers/pci/pcie/portdrv_core.c
> index 50a9522..1991aca 100644
> --- a/drivers/pci/pcie/portdrv_core.c
> +++ b/drivers/pci/pcie/portdrv_core.c
> @@ -491,7 +491,6 @@ 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);
>  }
>
>  /**
> diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c
> index 3a3ce40..ce89a9e8 100644
> --- a/drivers/pci/pcie/portdrv_pci.c
> +++ b/drivers/pci/pcie/portdrv_pci.c
> @@ -15,6 +15,7 @@
>  #include <linux/init.h>
>  #include <linux/aer.h>
>  #include <linux/dmi.h>
> +#include <linux/kexec.h>
>
>  #include "../pci.h"
>  #include "portdrv.h"
> @@ -143,6 +144,28 @@ 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)
> +{
> +       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 this is a kexec reboot, turn off Bus Master bit on the
> +        * device to tell it to not continue to do DMA. Don't touch
> +        * devices in D3cold or unknown states.
> +        * If it is not a kexec reboot, firmware will hit the PCI
> +        * devices with big hammer and stop their DMA any way.
> +        */
> +       if (kexec_in_progress && (dev->current_state <= PCI_D3hot))
> +               pci_disable_device(dev);
>  }
>
>  static pci_ers_result_t pcie_portdrv_error_detected(struct pci_dev *dev,
> @@ -211,7 +234,7 @@ static void pcie_portdrv_err_resume(struct pci_dev *dev)
>
>         .probe          = pcie_portdrv_probe,
>         .remove         = pcie_portdrv_remove,
> -       .shutdown       = pcie_portdrv_remove,
> +       .shutdown       = pcie_portdrv_shutdown,
>
>         .err_handler    = &pcie_portdrv_err_handler,
>
> --
> 1.8.3.1