Re: [PATCH v2 1/1] PCI: brcmstb: Fix regression regarding missing PCIe linkup

[Cyril Brulebois <kibi@debian.org>]

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Hi Jim,

Jim Quinlan <jim2101024@gmail.com> (2022-05-28):
> commit 93e41f3fca3d ("PCI: brcmstb: Add control of subdevice voltage regulators")
> 
> introduced a regression on the PCIe RPi4 Compute Module.  If the PCIe
> root port DT node described in [2] was missing, no linkup would be attempted,
> and subsequent accesses would cause a panic because this particular PCIe HW
> causes a CPU abort on illegal accesses (instead of returning 0xffffffff).
> 
> We fix this by allowing the DT root port node to be missing, as it behaved
> before the original patchset messed things up.
> 
> In addition, two small changes are made:
> 
>   1. Having pci_subdev_regulators_remove_bus() call
>      regulator_bulk_free() in addtion to regulator_bulk_disable().
>   2. Having brcm_pcie_add_bus() return 0 if there is an
>      error in calling pci_subdev_regulators_add_bus().
>      Instead, we dev_err() and turn on our refusal mode instead.
> 
> It would be best if this commit were tested by someone with a Rpi CM4
> platform, as that is how the regression was found.  I have only emulated
> the problem and fix on different platform.

Testing is less flawless than it was with the earlier version, but this
might be related to the fact master has moved a lot since then (from
v5.18-rcX to open merge window).

Overall, it's still a net win over the status quo (broken boot).


Applying your patch on 664a393a2663a0f62fc1b18157ccae33dcdbb8c8 and
performing cold boots is mostly fine:
 - without anything on the PCIe slot;
 - with a PCIe→quad-USB extension board, a USB keyboard and a USB stick
   (both work fine).

However, with an empty PCIe slot, I'm no longer able to perform the
following (which was rock solid, and has been used in all my testing up
to now):
 - boot the exact same Debian stable image as before (running v5.10.y if
   that matters);
 - deploy the patched kernel;
 - enable serial console;
 - reboot into the patched kernel.

PCI-related messages, a call trace, and broken storage:

    [    3.425331] brcm-pcie fd500000.pcie: host bridge /scb/pcie@7d500000 ranges:
    [    3.425353] brcm-pcie fd500000.pcie:   No bus range found for /scb/pcie@7d500000, using [bus 00-ff]
    [    3.425388] brcm-pcie fd500000.pcie:      MEM 0x0600000000..0x0603ffffff -> 0x00f8000000
    [    3.425420] brcm-pcie fd500000.pcie:   IB MEM 0x0000000000..0x003fffffff -> 0x0400000000
    [    3.426229] brcm-pcie fd500000.pcie: PCI host bridge to bus 0000:00
    [    3.426243] pci_bus 0000:00: root bus resource [bus 00-ff]
    [    3.426255] pci_bus 0000:00: root bus resource [mem 0x600000000-0x603ffffff] (bus address [0xf8000000-0xfbffffff])
    [    3.426303] pci 0000:00:00.0: [14e4:2711] type 01 class 0x060400
    [    3.426398] pci 0000:00:00.0: PME# supported from D0 D3hot
    [    3.428797] pci 0000:00:00.0: bridge configuration invalid ([bus 00-00]), reconfiguring
    [    3.745909] brcm-pcie fd500000.pcie: link down
    [    3.747915] pci_bus 0000:01: busn_res: [bus 01-ff] end is updated to 01
    [    3.747944] pci 0000:00:00.0: PCI bridge to [bus 01]
    [    3.748294] pcieport 0000:00:00.0: PME: Signaling with IRQ 23
    [    3.748691] pcieport 0000:00:00.0: AER: enabled with IRQ 23
    [    3.749201] pci_bus 0000:01: busn_res: [bus 01] is released
    [    3.749462] pci_bus 0000:00: busn_res: [bus 00-ff] is released
    …
    [    5.617308] irq 35: nobody cared (try booting with the "irqpoll" option)
    [    5.617335] CPU: 0 PID: 127 Comm: systemd-udevd Not tainted 5.18.0+ #1
    [    5.617350] Hardware name: Raspberry Pi Compute Module 4 Rev 1.0 (DT)
    [    5.617358] Call trace:
    [    5.617362]  dump_backtrace+0xc0/0x130
    [    5.617386]  show_stack+0x24/0x70
    [    5.617396]  dump_stack_lvl+0x68/0x84
    [    5.617415]  dump_stack+0x18/0x34
    [    5.617426]  __report_bad_irq+0x54/0x16c
    [    5.617436]  note_interrupt+0x324/0x41c
    [    5.617445]  handle_irq_event+0xc0/0x180
    [    5.617460]  handle_fasteoi_irq+0xc8/0x1fc
    [    5.617468]  generic_handle_domain_irq+0x38/0x50
    [    5.617481]  gic_handle_irq+0x68/0xa0
    [    5.617489]  call_on_irq_stack+0x2c/0x60
    [    5.617500]  do_interrupt_handler+0x88/0x90
    [    5.617511]  el0_interrupt+0x58/0x124
    [    5.617526]  __el0_irq_handler_common+0x18/0x2c
    [    5.617538]  el0t_64_irq_handler+0x10/0x20
    [    5.617549]  el0t_64_irq+0x18c/0x190
    [    5.617558] handlers:
    [    5.617563] [<(____ptrval____)>] sdhci_irq [sdhci] threaded [<(____ptrval____)>] sdhci_thread_irq [sdhci]
    [    5.617613] Disabling IRQ #35
    …
    [   15.581894] mmc0: Timeout waiting for hardware cmd interrupt.
    [   15.581914] mmc0: sdhci: ============ SDHCI REGISTER DUMP ===========
    [   15.581920] mmc0: sdhci: Sys addr:  0x00000000 | Version:  0x00001002
    [   15.581931] mmc0: sdhci: Blk size:  0x00000000 | Blk cnt:  0x00000000
    [   15.581937] mmc0: sdhci: Argument:  0x00000c00 | Trn mode: 0x00000000
    [   15.581944] mmc0: sdhci: Present:   0x1fff0000 | Host ctl: 0x00000001
    [   15.581951] mmc0: sdhci: Power:     0x0000000f | Blk gap:  0x00000080
    [   15.581957] mmc0: sdhci: Wake-up:   0x00000000 | Clock:    0x00007d07
    [   15.581964] mmc0: sdhci: Timeout:   0x00000000 | Int stat: 0x00018000
    [   15.581971] mmc0: sdhci: Int enab:  0x00ff1003 | Sig enab: 0x00ff1003
    [   15.581976] mmc0: sdhci: ACmd stat: 0x00000000 | Slot int: 0x00000001
    [   15.581982] mmc0: sdhci: Caps:      0x45ee6432 | Caps_1:   0x0000a525
    [   15.581988] mmc0: sdhci: Cmd:       0x0000341a | Max curr: 0x00080008
    [   15.581996] mmc0: sdhci: Resp[0]:   0x00000000 | Resp[1]:  0x00000000
    [   15.582001] mmc0: sdhci: Resp[2]:   0x00000000 | Resp[3]:  0x00000000
    [   15.582005] mmc0: sdhci: Host ctl2: 0x00000000
    [   15.582011] mmc0: sdhci: ADMA Err:  0x00000000 | ADMA Ptr: 0x00000000
    [   15.582016] mmc0: sdhci: ============================================

This last part gets repeated over and over, and storage (external SD
card) never comes up. I can share fuller logs if that's desirable. I can
also test booting with irqpoll if that's desirable. Or anything else that
might help.


I did check that applying the same patch on top of the v5.18 tag gives
good results (cold boots and reboots are fine, with or without an empty
PCIe slot, as that was the case during earlier test sessions), so I'd
guess something changed since then, and makes reboots more brittle than
they used to be.

I can also check applying the v1 patch on top of master and compare
results, to give a different perspective.

But I'd also be happy to get some directions as to which test(s) would
be most beneficial, which would help me cut down on combinatorics.


Cheers,
-- 
Cyril Brulebois (kibi@debian.org)            <https://debamax.com/>
D-I release manager -- Release team member -- Freelance Consultant

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