linux-kernel - Re: [RFC PATCH] PCI/portdrv: No need to call pci_disable

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Message-ID: <da291cff-4f56-c849-f0c3-3af1115bd06e@loongson.cn>
Date:   Fri, 11 Sep 2020 11:19:53 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Oliver O'Halloran <oohall@...il.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Huacai Chen <chenhc@...ote.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [RFC PATCH] PCI/portdrv: No need to call pci_disable_device()
 during shutdown

On 09/11/2020 10:35 AM, Oliver O'Halloran wrote:
> On Fri, Sep 11, 2020 at 11:55 AM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>> On 09/11/2020 04:21 AM, Bjorn Helgaas wrote:
>>> [+cc Huacai]
>>>
>>> On Thu, Sep 10, 2020 at 02:41:39PM -0500, Bjorn Helgaas wrote:
>>>> On Sat, Sep 05, 2020 at 04:33:26PM +0800, Tiezhu Yang wrote:
>>>>> 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 seems unnecessary, so just remove it.
>>>> I would like to get rid of the portdrv completely by folding its
>>>> functionality into the PCI core itself, so there would be no portdrv
>>>> probe or remove.
>>>>
>>>> Does this solve a problem?
>> Yes, sometimes it can not shutdown or reboot normally with
>> pci_disable_device().
> Do you have any more details about what goes wrong here?

This issue is related with the operation "pci_command &= 
~PCI_COMMAND_MASTER;"
in the following function:

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.

> Leaving
> devices enabled when actually shutting down probably doesn't matter.

Yes, I think so too.

> However, .shutdown() is also used when kexec()ing into a new kernel
> and we probably should be disabling devices before handing over to the
> new kernel.
>
> Is the real issue that we're closing the bridge windows before the
> endpoint drivers have had a chance to clean up?

I notice that check kexec_in_progress first before call pci_disable_devie()
in pci_device_shutdown(), can we do the similar thing in pcie?

drivers/pci/pci-driver.c
static void pci_device_shutdown(struct device *dev)
{
     struct pci_dev *pci_dev = to_pci_dev(dev);
     struct pci_driver *drv = pci_dev->driver;

     pm_runtime_resume(dev);

     if (drv && drv->shutdown)
         drv->shutdown(pci_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);
}

Something like this:

diff --git a/drivers/pci/pcie/portdrv_core.c 
b/drivers/pci/pcie/portdrv_core.c
index 50a9522..3de1dab 100644
--- a/drivers/pci/pcie/portdrv_core.c
+++ b/drivers/pci/pcie/portdrv_core.c
@@ -491,7 +491,8 @@ 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);
+       if (kexec_in_progress && (pci_dev->current_state <= PCI_D3hot))
+               pci_disable_device(dev);
  }

  /**

>
> Oliver