Re: [PATCH] PCI, pciehp: Turn on link a while to workaround presense detection

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On Fri, Dec 6, 2013 at 1:22 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
> During hotplug test on platform, found slot status register does not
> report present status correctly. That present bit does not get cleared
> even after that card is removed.
>
> That problem is caused by commit:
> | commit 2debd9289997fc5d1c0043b41201a8b40d5e11d0
> |
> |    PCI: pciehp: Disable/enable link during slot power off/on
>
> It looks like chipset bug, that PresDet bit is "OR" operation between
> sideband input from FPGA, and chipset inband detection from pcie link.

This doesn't sound like a chipset bug.  It sounds like exactly what
the spec describes: "Presence Detect State – This bit indicates the
presence of an adapter in the slot, reflected by the logical “OR” of
the Physical Layer in-band presence detect mechanism and, if present,
any out-of-band presence detect mechanism defined for the slot’s
corresponding form factor" (PCIe 3.0, sec 7.8.11).

So I want to fix this pciehp problem, but between 2debd9289997 and
this patch, pciehp_power_off_slot() is accumulating warts that make it
look like we're just reacting to things that break rather than making
a robust design to start with.

> It does not like if we disable pcie link at first and power off
> other side device, and it has input from inband detection
> always 1.
>
> Workaround: Try turn on link a while after power off.
>
> After this patch, PresDet report correct status when removing or adding
> card later.
>
> Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>
> Cc: Kenji Kaneshige <kaneshige.kenji@xxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> 3.4+
>
> ---
>  drivers/pci/hotplug/pciehp_hpc.c |    9 +++++++++
>  1 file changed, 9 insertions(+)
>
> Index: linux-2.6/drivers/pci/hotplug/pciehp_hpc.c
> ===================================================================
> --- linux-2.6.orig/drivers/pci/hotplug/pciehp_hpc.c
> +++ linux-2.6/drivers/pci/hotplug/pciehp_hpc.c
> @@ -637,6 +637,15 @@ int pciehp_power_off_slot(struct slot *
>         }
>         ctrl_dbg(ctrl, "%s: SLOTCTRL %x write cmd %x\n", __func__,
>                  pci_pcie_cap(ctrl->pcie->port) + PCI_EXP_SLTCTL, slot_cmd);
> +
> +       /*
> +        * Enable link for a while so chipset could settle down
> +        * inband presence detection logic
> +        */
> +       pciehp_link_enable(ctrl);
> +       msleep(20);
> +       pciehp_link_disable(ctrl);
> +
>         return 0;
>  }
>
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