Re: [PATCH 06/18] PCI: pciehp: Enable DLLSC interrupt only if supported

Lukas Wunner
2022-05-14T09:14:09Z

On Fri, May 13, 2022 at 06:57:29PM +0200, Pali Rohár wrote:
> To answer your questions: Config space of Aardvark Root Port does not
> conform to PCIe base spec. It does not implement DLLLARC, nor DLLSCE and
> lot of other bits. Plus it has Type 0 header (not Type 1). And due to
> these reasons, pci-aardvark.c driver implements "emulation" of the
> Root Port and implements some of the functionality via custom aardvark
> registers. So Root Port would be presented to kernel and also to
> userspace as PCI Bridge device with Type 1 header and with PCIe
> registers required by linux kernel.
>
> During my testing of kernel hotplug code last year, I figured out that
> kernel was waiting for event which never happened. And so it was needed
> to "fix" kernel to not try to enable DLLSCE because it did nothing.

Could you please reproduce this and add the following on the command line:

log_buf_len=10M pciehp.pciehp_debug=1 dyndbg="file pciehp* +p"
ignore_loglevel

Then open a bug at bugzilla.kernel.org, attach full dmesg output
as well as full "lspci -vv" output and send the bugzilla link to me.

(Obviously, revert patches 6 and 7 when trying to reproduce it.)

So a PDC event should be sufficient to bring the slot up or down,
a DLLSC event should not be necessary. Enabling DLLSC should not
make a difference on a controller which doesn't support it.
I just double-checked the code and I do not see where we'd wait
for a DLLSC event which never comes.

Don't worry, if we come to the conclusion that your proposed fix
is the only solution, I'm fine with it, but at this point I'd
like to get a better understanding what is really going on.
Perhaps there is some other issue in pciehp that this patch
just papers over. Once you provide the dmesg debug output
I'll be able to analyze that.

Thanks!

Lukas