linux-kernel - Re: [PATCH] pci: Disable slot presence detection around bus reset

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Date:	Thu, 14 Feb 2013 15:17:50 -0700
From:	Alex Williamson <alex.williamson@...hat.com>
To:	bhelgaas@...gle.com
Cc:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pci: Disable slot presence detection around bus reset

On Thu, 2013-02-14 at 11:37 -0700, Alex Williamson wrote:
> A bus reset can trigger a presence detection change and result in a
> suprise hotplug.  This is generally not what we want to happen when
> trying to reset a device.  Disable the presence detection control on
> on bridges around bus reset.
> 
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> ---
>  drivers/pci/pci.c |   29 ++++++++++++++++++++++++-----
>  1 file changed, 24 insertions(+), 5 deletions(-)


Hmm, this doesn't seem to be sufficient, still seeing it
occasionally :-\

> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 5cb5820..c1f7d77 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3229,8 +3229,8 @@ static int pci_pm_reset(struct pci_dev *dev, int probe)
>  
>  static int pci_parent_bus_reset(struct pci_dev *dev, int probe)
>  {
> -	u16 ctrl;
> -	struct pci_dev *pdev;
> +	u16 ctrl, flags, sltctl = 0;
> +	struct pci_dev *pdev, *bridge;
>  
>  	if (pci_is_root_bus(dev->bus) || dev->subordinate || !dev->bus->self)
>  		return -ENOTTY;
> @@ -3242,15 +3242,34 @@ static int pci_parent_bus_reset(struct pci_dev *dev, int probe)
>  	if (probe)
>  		return 0;
>  
> -	pci_read_config_word(dev->bus->self, PCI_BRIDGE_CONTROL, &ctrl);
> +	bridge = dev->bus->self;
> +
> +	/*
> +	 * If the parent device supports a slot with presence detection
> +	 * change enabled, holding the bus in reset can trigger that and
> +	 * cause an unwanted surprise removal.  Disable presence detection
> +	 * around the bus reset.
> +	 */
> +	pcie_capability_read_word(bridge, PCI_EXP_FLAGS, &flags);
> +	if (flags & PCI_EXP_FLAGS_SLOT) {
> +		pcie_capability_read_word(bridge, PCI_EXP_SLTCTL, &sltctl);
> +		if (sltctl & PCI_EXP_SLTCTL_PDCE)
> +			pcie_capability_write_word(bridge, PCI_EXP_SLTCTL,
> +						sltctl & ~PCI_EXP_SLTCTL_PDCE);
> +	}
> +
> +	pci_read_config_word(bridge, PCI_BRIDGE_CONTROL, &ctrl);
>  	ctrl |= PCI_BRIDGE_CTL_BUS_RESET;
> -	pci_write_config_word(dev->bus->self, PCI_BRIDGE_CONTROL, ctrl);
> +	pci_write_config_word(bridge, PCI_BRIDGE_CONTROL, ctrl);
>  	msleep(100);
>  
>  	ctrl &= ~PCI_BRIDGE_CTL_BUS_RESET;
> -	pci_write_config_word(dev->bus->self, PCI_BRIDGE_CONTROL, ctrl);
> +	pci_write_config_word(bridge, PCI_BRIDGE_CONTROL, ctrl);
>  	msleep(100);
>  
> +	if (sltctl & PCI_EXP_SLTCTL_PDCE)
> +		pcie_capability_write_word(bridge, PCI_EXP_SLTCTL, sltctl);
> +
>  	return 0;
>  }
>  
> 



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