On Tue, Jun 17, 2014 at 1:27 PM, Myron Stowe <myron.stowe@xxxxxxxxxx> wrote:
> During PCIe hot-plug initialization - pciehp_probe - data structures
> related to slot capabilities are set up. As part of this set up, ISRs are
> put in place to handle slot events and all event bits are cleared out.
>
> This patch adds the Data Link Layer State Changed (PCI_EXP_SLTSTA_DLLSC)
> Slot Status bit to the event bits that are cleared out during
> initialization.
I think this is related to e48f1b67f668 ("PCI: pciehp: Use link change
notifications for hot-plug and removal"). Prior to that, pcie_isr()
didn't look at the PCI_EXP_SLTSTA_DLLSC bit.
Apparently there's a non-public report of spurious messages like this
at boot-time, with no actual hotplug events:
pciehp 0000:82:04.0:pcie24: slot(4): Link Up event
pciehp 0000:82:04.0:pcie24: Device 0000:83:00.0 already exists at
0000:83:00, cannot hot-add
pciehp 0000:82:04.0:pcie24: Cannot add device at 0000:83:00
Device 0000:83:00.0 was enumerated previously, during the normal PCI
device enumeration. I suspect DLLSC was set by the hardware when the
link came up after power-on, and it remained set until Linux booted.
Then when we take the first pciehp interrupt, we notice DLLSC is set
and think it's a new link state change.
This might be system-specific, because some BIOSes might clear DLLSC
before handing off to the OS. Or my theory might be all wet.
But I think we should clear DLLSC in any case. We clear all the other
RW1C bits in Slot Status, and I think we should clear DLLSC as well.
I'd like to include a bugzilla or mailing list reference for the
spurious message, and I'd also like confirmation that this changes
actually fixes it.
Bjorn
> Reference:
> PCI-SIG. PCI Express Base Specification Revision 4.0 Version 0.3
> (PCI-SIG, 2014): 7.8.11. Slot Status Register (Offset 1Ah).
>
> Signed-off-by: Myron Stowe <myron.stowe@xxxxxxxxxx>
> ---
>
> drivers/pci/hotplug/pciehp_hpc.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index 42914e0..0568416 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -794,7 +794,7 @@ struct controller *pcie_init(struct pcie_device *dev)
> pcie_capability_write_word(pdev, PCI_EXP_SLTSTA,
> PCI_EXP_SLTSTA_ABP | PCI_EXP_SLTSTA_PFD |
> PCI_EXP_SLTSTA_MRLSC | PCI_EXP_SLTSTA_PDC |
> - PCI_EXP_SLTSTA_CC);
> + PCI_EXP_SLTSTA_CC | PCI_EXP_SLTSTA_DLLSC);
>
> /* Disable software notification */
> pcie_disable_notification(ctrl);
>
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