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

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Date:   Mon, 14 Sep 2020 06:06:25 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Konstantin Khlebnikov <khlebnikov@...nvz.org>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Vivek Goyal <vgoyal@...hat.com>, oohall@...il.com,
        rafael.j.wysocki@...el.com, Xuefeng Li <lixuefeng@...ngson.cn>,
        Huacai Chen <chenhc@...ote.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2] PCI/portdrv: Only disable Bus Master on kexec
 reboot and connected PCI devices

On Mon, Sep 14, 2020 at 04:29:10AM +0800, Tiezhu Yang wrote:
> --- a/drivers/pci/pcie/portdrv_pci.c
> +++ b/drivers/pci/pcie/portdrv_pci.c
> @@ -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);

The last portion of this function is already executed afterwards by
pci_device_shutdown().  You don't need to duplicate it here:

device_shutdown()
  dev->bus->shutdown() == pci_device_shutdown()
    drv->shutdown() == pcie_portdrv_shutdown()
      pci_disable_device()
    pci_disable_device()

Thanks,

Lukas