linux-kernel - Re: [PATCH v5 4/9] pci: Add slot reset option to pci_dev

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Date:	Wed, 14 Aug 2013 15:22:17 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Alex Duyck <alexander.h.duyck@...el.com>,
	Don Dutile <ddutile@...hat.com>,
	Takao Indoh <indou.takao@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 4/9] pci: Add slot reset option to pci_dev_reset

On Thu, Aug 8, 2013 at 2:09 PM, Alex Williamson
<alex.williamson@...hat.com> wrote:
> If the hotplug controller provides a way to reset a slot, use that
> before a direct parent bus reset.  Like the bus reset option, this is
> only available when a single pci_dev occupies the slot.
>
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> ---
>  drivers/pci/pci.c |   34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index d468608..9407aab 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -22,6 +22,7 @@
>  #include <linux/interrupt.h>
>  #include <linux/device.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/pci_hotplug.h>
>  #include <asm-generic/pci-bridge.h>
>  #include <asm/setup.h>
>  #include "pci.h"
> @@ -3256,6 +3257,35 @@ static int pci_parent_bus_reset(struct pci_dev *dev, int probe)
>         return 0;
>  }
>
> +static int pci_reset_hotplug_slot(struct hotplug_slot *hotplug, int probe)
> +{
> +       int rc = -ENOTTY;
> +
> +       if (!hotplug || !try_module_get(hotplug->ops->owner))
> +               return rc;
> +
> +       if (hotplug->ops->reset_slot)
> +               rc = hotplug->ops->reset_slot(hotplug, probe);
> +
> +       module_put(hotplug->ops->owner);
> +
> +       return rc;
> +}
> +
> +static int pci_dev_reset_slot_function(struct pci_dev *dev, int probe)
> +{
> +       struct pci_dev *pdev;
> +
> +       if (dev->subordinate || !dev->slot)
> +               return -ENOTTY;
> +
> +       list_for_each_entry(pdev, &dev->bus->devices, bus_list)
> +               if (pdev != dev && pdev->slot == dev->slot)
> +                       return -ENOTTY;
> +
> +       return pci_reset_hotplug_slot(dev->slot->hotplug, probe);

I don't think this is hotplug-safe.  It looks like pci_bus_sem might
be the right semaphore to hold while verifying that we won't reset any
unintended devices.  But I think most users of the bus->devices list
are unprotected, so there's no point in trying to fix just this one.

> +}
> +
>  static int __pci_dev_reset(struct pci_dev *dev, int probe)
>  {
>         int rc;
> @@ -3278,6 +3308,10 @@ static int __pci_dev_reset(struct pci_dev *dev, int probe)
>         if (rc != -ENOTTY)
>                 goto done;
>
> +       rc = pci_dev_reset_slot_function(dev, probe);
> +       if (rc != -ENOTTY)
> +               goto done;
> +
>         rc = pci_parent_bus_reset(dev, probe);
>  done:
>         return rc;
>
--
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