Re: [PATCH v1] drivers: pci: introduce configurable delay for Rockchip PCIe bus scan

[Peter Geis]

On Fri, May 12, 2023 at 9:24 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> [+cc ARM64 folks, in case you have abort handling tips; thread at:
> https://lore.kernel.org/r/20230509153912.515218-1-vincenzopalazzodev@xxxxxxxxx]
>
> Pine64 RockPro64 panics while enumerating some PCIe devices.  Adding a
> delay avoids the panic.  My theory is a PCIe Request Retry Status to a
> Vendor ID config read causes an abort that we don't handle.
>
> > On Tue, May 09, 2023 at 05:39:12PM +0200, Vincenzo Palazzo wrote:
> >> ...
> >> [    1.229856] SError Interrupt on CPU4, code 0xbf000002 -- SError
> >> [    1.229860] CPU: 4 PID: 1 Comm: swapper/0 Not tainted 5.9.9-2.0-MANJARO-ARM
> >> #1
> >> [    1.229862] Hardware name: Pine64 RockPro64 v2.1 (DT)
> >> [    1.229864] pstate: 60000085 (nZCv daIf -PAN -UAO BTYPE=--)
> >> [    1.229866] pc : rockchip_pcie_rd_conf+0xb4/0x270
> >> [    1.229868] lr : rockchip_pcie_rd_conf+0x1b4/0x270
> >> ...
> >> [    1.229939] Kernel panic - not syncing: Asynchronous SError Interrupt
> >> ...
> >> [    1.229955]  nmi_panic+0x8c/0x90
> >> [    1.229956]  arm64_serror_panic+0x78/0x84
> >> [    1.229958]  do_serror+0x15c/0x160
> >> [    1.229960]  el1_error+0x84/0x100
> >> [    1.229962]  rockchip_pcie_rd_conf+0xb4/0x270
> >> [    1.229964]  pci_bus_read_config_dword+0x6c/0xd0
> >> [    1.229966]  pci_bus_generic_read_dev_vendor_id+0x34/0x1b0
> >> [    1.229968]  pci_scan_single_device+0xa4/0x144
>
> On Fri, May 12, 2023 at 12:46:21PM +0200, Vincenzo Palazzo wrote:
> > ... Is there any way to tell the kernel "hey we need some more time
> > here"?
>
> We enumerate PCI devices by trying to read the Vendor ID of every
> possible device address (see pci_scan_slot()).  On PCIe, if a device
> doesn't exist at that address, the Vendor ID config read will be
> terminated with Unsupported Request (UR) status.  This is normal
> and happens every time we enumerate devices.
>
> The crash doesn't happen every time we enumerate, so I don't think
> this UR is the problem.  Also, if it *were* the problem, adding a
> delay would not make any difference.

Is this behavior different if there is a switch device forwarding on
the UR? On rk3399 switches are completely non-functional because of
the panic, which is observed in the output of the dmesg in [2] with
the hack patch enabled. Considering what you just described it looks
like the forwarded UR for each non-existent device behind the switch
is causing an serror.

>
> There *is* a way for a PCIe device to say "I need more time".  It does
> this by responding to that Vendor ID config read with Request Retry
> Status (RRS, aka CRS in older specs), which means "I'm not ready yet,
> but I will be ready in the future."  Adding a delay would definitely
> make a difference here, so my guess is this is what's happening.
>
> Most root complexes return ~0 data to the CPU when a config read
> terminates with UR or RRS.  It sounds like rockchip does this for UR
> but possibly not for RRS.
>
> There is a "RRS Software Visibility" feature, which is supposed to
> turn the RRS into a special value (Vendor ID == 0x0001), but per [1],
> rockchip doesn't support it (lspci calls it "CRSVisible").
>
> But the CPU load instruction corresponding to the config read has to
> complete by reading *something* or else be aborted.  It sounds like
> it's aborted in this case.  I don't know the arm64 details, but if we
> could catch that abort and determine that it was an RRS and not a UR,
> maybe we could fabricate the magic RRS 0x0001 value.
>
> imx6q_pcie_abort_handler() does something like that, although I think
> it's for arm32, not arm64.  But obviously we already catch the abort
> enough to dump the register state and panic, so maybe there's a way to
> extend that?

Perhaps a hook mechanism that allows drivers to register with the
serror handler and offer to handle specific errors before the generic
code causes the system panic?

Very Respectfully,
Peter Geis

[2] https://lore.kernel.org/linux-pci/CAMdYzYqn3L7x-vc+_K6jG0EVTiPGbz8pQ-N1Q1mRbcVXE822Yg@xxxxxxxxxxxxxx/

>
> Bjorn
>
> [1] https://lore.kernel.org/linux-pci/CAMdYzYpOFAVq30N+O2gOxXiRtpoHpakFg3LKq3TEZq4S6Y0y0g@xxxxxxxxxxxxxx/