Re: [PATCH] PCI: quirk for preventing bus reset on TI C667X

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Alex, Murali, Kishon]

On Tue, Jan 12, 2021 at 03:36:43PM +0000, Antti Järvinen wrote:
> TI C667X does not support bus/hot reset.
> See https://e2e.ti.com/support/processors/f/791/t/954382

You can cite the URL as the source, but the URL will eventually become
stale, so let's include the relevant details here directly.  

From the forum, it looks like the device doesn't respond after a
reset (config accesses return ~0).  It seems somewhat surprising that
something as basic as a reset would be completely broken.  I wonder if
we're not doing the reset correctly.

It looks like we would probably be trying a Secondary Bus Reset using
the bridge leading to the C667X.  Can you confirm?  Wonder if you
could try doing what pci_reset_secondary_bus() does by hand:

  # BRIDGE=...                              # PCI address, e.g., 00:1c.0
  # C667X=...
  # setpci -s$C667X VENDOR_ID.w
  # setpci -s$BRIDGE BRIDGE_CONTROL.w       # prints "val"
  # setpci -s$BRIDGE BRIDGE_CONTROL.w=      # val | 0x40 (set SBR)
  # sleep 1
  # setpci -s$BRIDGE BRIDGE_CONTROL.w=      # val (clear SBR)
  # sleep 1
  # setpci -s$C667X VENDOR_ID.w=0
  # setpci -s$C667X VENDOR_ID.w

If we use this quirk and avoid the reset, I assume that means
assigning the device to VMs with VFIO will leak state between VMs?

> Signed-off-by: Antti Järvinen <antti.jarvinen@gmail.com>
> ---
>  drivers/pci/quirks.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 653660e3ba9e..c8fcf24c5bd0 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -3578,6 +3578,12 @@ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x0034, quirk_no_bus_reset);
>   */
>  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_CAVIUM, 0xa100, quirk_no_bus_reset);
>  
> +/*
> + * Some TI keystone C667X devices do no support bus/hot reset.
> + * https://e2e.ti.com/support/processors/f/791/t/954382
> + */
> +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_TI, 0xb005, quirk_no_bus_reset);
> +
>  static void quirk_no_pm_reset(struct pci_dev *dev)
>  {
>  	/*
> -- 
> 2.17.1
>