On Tue, Oct 24, 2017 at 02:09:14PM +0300, Mika Westerberg wrote:
> During surprise hot-unplug the device is not there anymore. When that
> happens we read 0xffffffff from the registers and pciehp_unconfigure_device()
> might inadvertently think the device is a display device because bridge
> control register returns 0xff refusing to remove it:
>
> pciehp 0000:00:1c.0:pcie004: Slot(0): Link Down
> pciehp 0000:00:1c.0:pcie004: Slot(0): Card present
> pciehp 0000:00:1c.0:pcie004: Cannot remove display device 0000:01:00.0
>
> This causes the hotplug functionality to leave the hierarcy untouched
> preventing further hotplug operations.
>
> Fix this so that we first compare the read bctl value against 0xffff
> (device is not present anymore) before determining whether the device is
> a display or not.
>
> Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> ---
> Hi Bjorn,
>
> This is an updated version of the patch 8/8 in my "PCI: Improvements for
> native PCIe hotplug" patch series and applies on top of pci.git/pci/hotplug.
>
> We now just check bctl against 0xffff before preventing removal of the
> "display" device.
>
> I'm inclined to remove the whole check of "display" device because I don't
> see any reason for it to be there in the first place. This code is pretty
> much duplicated from shpchp_pci.c where it might make some sense.
Yeah, I don't understand this at all. If the device is gone, it's
gone, and complaining about it being a display device isn't going to
make it come back. I don't know the history of that check, but I
agree that it might make sense to remove it altogether.
The message (and consequently your changelog) also seem misleading
because we're removing *dev*, which in this case is a bridge that
might lead to a display device. But it's not a display device itself.
> drivers/pci/hotplug/pciehp_pci.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/hotplug/pciehp_pci.c b/drivers/pci/hotplug/pciehp_pci.c
> index 2a1ca020cf5a..5225b12c5a75 100644
> --- a/drivers/pci/hotplug/pciehp_pci.c
> +++ b/drivers/pci/hotplug/pciehp_pci.c
> @@ -79,7 +79,6 @@ int pciehp_configure_device(struct slot *p_slot)
> int pciehp_unconfigure_device(struct slot *p_slot)
> {
> int rc = 0;
> - u8 bctl = 0;
> u8 presence = 0;
> struct pci_dev *dev, *temp;
> struct pci_bus *parent = p_slot->ctrl->pcie->port->subordinate;
> @@ -102,8 +101,10 @@ int pciehp_unconfigure_device(struct slot *p_slot)
> bus_list) {
> pci_dev_get(dev);
> if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE && presence) {
> - pci_read_config_byte(dev, PCI_BRIDGE_CONTROL, &bctl);
> - if (bctl & PCI_BRIDGE_CTL_VGA) {
> + u16 bctl = 0;
> +
> + pci_read_config_word(dev, PCI_BRIDGE_CONTROL, &bctl);
> + if (bctl != 0xffff && (bctl & PCI_BRIDGE_CTL_VGA)) {
> ctrl_err(ctrl,
> "Cannot remove display device %s\n",
> pci_name(dev));
> --
> 2.14.2
>
