linux-kernel - Re: [PATCH v2] PCI: pciehp: Check link state before accessing device during removal

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Date:	Sun, 7 Dec 2014 22:15:31 -0800
From:	Rajat Jain <rajatxjain@...il.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Cc:	Rajat Jain <rajatjain@...iper.net>,
	Guenter Roeck <groeck@...iper.net>,
	Rajat Jain <rajatxjain@...il.com>
Subject: Re: [PATCH v2] PCI: pciehp: Check link state before accessing device
 during removal

Hello Bjorn,

Just checking if you got a chance to look at this.

Thanks,

Rajat


On Thu, Nov 20, 2014 at 2:54 PM, Rajat Jain <rajatxjain@...il.com> wrote:
> While removing a card, we can't assume the presence to mean that the
> access to card is OK. That is because the cause of removal may be a
> link down event, and the card may still be physically present. Thus,
> instead of presence, use the link state to decide whether or not it is
> OK to access the card devices.
>
> Here are the problem symptoms:
> During the removal of a card due to link down, sometimes the following
> error is seen (because pciehp_unconfigure_device() reads 0xFF from
> bridge control register as the link is down, which cause it to assume
> that the VGA bit is set):
>
> pciehp 0000:21:05.0:pcie24: pcie_isr: intr_loc 100
> pciehp 0000:21:05.0:pcie24: Data Link Layer State change
> pciehp 0000:21:05.0:pcie24: slot(5): Link Down event
> pciehp 0000:21:05.0:pcie24: Disabling domain:bus:device=0000:60:00
> pciehp 0000:21:05.0:pcie24: pciehp_unconfigure_device: domain:bus:dev = 0000:60:00
> pciehp 0000:21:05.0:pcie24: Cannot remove display device 0000:60:00.0
>
> Ofcourse, when the link comes back up, the device addition fails too:
>
> pciehp 0000:21:05.0:pcie24: pcie_isr: intr_loc 100
> pciehp 0000:21:05.0:pcie24: Data Link Layer State change
> pciehp 0000:21:05.0:pcie24: pciehp_check_link_active: lnk_status = 6011
> pciehp 0000:21:05.0:pcie24: slot(5): Link Up event
> pciehp 0000:21:05.0:pcie24: Enabling domain:bus:device=0000:60:00
> pciehp 0000:21:05.0:pcie24: pciehp_check_link_active: lnk_status = 6011
> pciehp 0000:21:05.0:pcie24: pciehp_check_link_status: lnk_status = 6011
> pciehp 0000:21:05.0:pcie24: Device 0000:60:00.0 already exists at 0000:60:00, cannot hot-add
> pciehp 0000:21:05.0:pcie24: Cannot add device at 0000:60:00
>
> The problem is not seen with this patch applied. The device removal and
> insertion works as expected.
>
> Signed-off-by: Rajat Jain <rajatxjain@...il.com>
> Signed-off-by: Rajat Jain <rajatjain@...iper.net>
> Signed-off-by: Guenter Roeck <groeck@...iper.net>
> ---
> v2: Use the already initialized "ctrl" instead of "p_slot->ctrl"
>
>  drivers/pci/hotplug/pciehp_pci.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/hotplug/pciehp_pci.c b/drivers/pci/hotplug/pciehp_pci.c
> index 9e69403..911f85b 100644
> --- a/drivers/pci/hotplug/pciehp_pci.c
> +++ b/drivers/pci/hotplug/pciehp_pci.c
> @@ -77,7 +77,7 @@ int pciehp_unconfigure_device(struct slot *p_slot)
>  {
>         int rc = 0;
>         u8 bctl = 0;
> -       u8 presence = 0;
> +       bool link_active = false;
>         struct pci_dev *dev, *temp;
>         struct pci_bus *parent = p_slot->ctrl->pcie->port->subordinate;
>         u16 command;
> @@ -85,7 +85,7 @@ int pciehp_unconfigure_device(struct slot *p_slot)
>
>         ctrl_dbg(ctrl, "%s: domain:bus:dev = %04x:%02x:00\n",
>                  __func__, pci_domain_nr(parent), parent->number);
> -       pciehp_get_adapter_status(p_slot, &presence);
> +       link_active = pciehp_check_link_active(ctrl);
>
>         pci_lock_rescan_remove();
>
> @@ -98,7 +98,7 @@ int pciehp_unconfigure_device(struct slot *p_slot)
>         list_for_each_entry_safe_reverse(dev, temp, &parent->devices,
>                                          bus_list) {
>                 pci_dev_get(dev);
> -               if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE && presence) {
> +               if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE && link_active) {
>                         pci_read_config_byte(dev, PCI_BRIDGE_CONTROL, &bctl);
>                         if (bctl & PCI_BRIDGE_CTL_VGA) {
>                                 ctrl_err(ctrl,
> @@ -114,7 +114,7 @@ int pciehp_unconfigure_device(struct slot *p_slot)
>                  * Ensure that no new Requests will be generated from
>                  * the device.
>                  */
> -               if (presence) {
> +               if (link_active) {
>                         pci_read_config_word(dev, PCI_COMMAND, &command);
>                         command &= ~(PCI_COMMAND_MASTER | PCI_COMMAND_SERR);
>                         command |= PCI_COMMAND_INTX_DISABLE;
> --
> 1.7.9.5
>
--
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