On 13.12.2022 00:49, Mika Westerberg wrote:
On Mon, Dec 12, 2022 at 04:10:16PM -0500, Alexander Motin wrote:
On 12.12.2022 15:32, Bjorn Helgaas wrote:
On Mon, Dec 12, 2022 at 1:36 PM Alexander Motin <mav@xxxxxxxxxxxxx> wrote:
In my AMD NTB case PCI topology looks this way:
+-[0000:80]-+-00.0
| +-01.1-[81-83]----00.0-[82-83]----00.0-[83]--+-00.0 Dummy
| | \-00.1 NTB
80:01.1 is the root bridge where the hot-plug happens. The 81:00.0
bridge in addition to memory windows has small 16KB BAR. But since it
is the only bridge on the bus, the function passes all available
resources down to its children. As result, that BAR fails to allocate.
And while that BAR seems not really needed, in some cases the
allocation error makes whole memory window to be disabled, that ends up
in NTB device driver attach failure.
Just out of the curiosity, is this PCIe or PCI topology?
All PCIe: hot-plug root <-> upstream <-> downstream <-> two endpoints.
Mika is working on what sounds like the same problem. His current
patch series is at
https://lore.kernel.org/linux-pci/20221130112221.66612-1-mika.westerberg@xxxxxxxxxxxxxxx/
We would appreciate your comments and testing as that series is developed.
Thank you, Bjorn. This definitely looks related, but as you've already
noted in your review there, present patch does not handle BARs of the bridge
itself, that I have in my case. I'd be happy to test the updated patch.
Please keep me in a loop.
I also agree with your comment that the same should be done in case of
multiple bridges. I am generally not sure the cases of single bridge or not
having hot-plug on this level should be any specific.
Yeah, I'm working on a new version of the patch series that should take
these into consideration. The challenge is that the code has been used
with the Thunderbolt/USB4 PCIe tunneling for some time already and we
don't want to break that either.
I'm also more than happy to test any patches regarding this if someone
else wants to work on it ;-)
I was kind of ready to dive in, I hate hacks and tunables to workaround
bugs. But as I have told, I see this code first time, so my solutions
may appear not right. But I'll help as I can, if needed.
--
Alexander Motin
