[Bug 290793] iovctl on mlx5en won't work

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=290793

--- Comment #7 from David BOYER <[email protected]> ---
(In reply to David BOYER from comment #3)

What's the call graph into this?

I had answered yesterday but just gor a message reading that a collision
occured.

I can only find mlx5_core/mlx5_main.c::request_bar -> pci_request_regions()
which ends up at the end of a loop in lkpi_pci_request_region().
==> The same for me

You made me actually look at Linux code and there you end up in
__pci_request_region()
which has the same checks at the beginning it seems:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/pci.c#n3935

So the problem is likely elsewhere in the LinuxKPI emulation or in mlx5.
My understanding is that pci_resource_len may return 0 on FreeBSD while linux
reports the right size.
Then, on FreeBSD, pci_request_region exits because pci_resource_len == 0,
bus_alloc_resource_any is not called and the memory is not allocated.
Why linux reports the right size ? 
https://wiki.osdev.org/PCI reads "To determine the amount of address space
needed by a PCI device, you must save the original value of the BAR, write a
value of all 1's to the register, then read it back. The amount of memory can
then be determined by masking the information bits, performing a bitwise NOT
('~' in C), and incrementing the value by 1. The original value of the BAR
should then be restored".
If I read correctly, this is done by pci_read_bases, found in
"drivers/pci/probe.c". It purpose is to find the BAR memory size.

Also the error logged:
mlx5_core2: lkpi_pci_request_region: failed to alloc bar 0 type 3 rid 16
comes from after that check?  So if it would fail and return we would not see
this?  Is that a secondary problem?
Yes, it comes after. Because the memory allocation step did not run
(pci_resource_len == 0).

If you say "On FreeBSD, the BAR size of VFs can temporarily be 0 and."
Would we assume mlx5core to only call pci_request_regions() once they are
properly initialized?
I guess we can say they are not properly initialized because it is done by the
kernel (on linux) not by the driver itself.

Please note that I am not an expert at all and had not read sourcecode of linux
and FreeBSD before, so I may be wrong somewhere, especially in my wording.

-- 
You are receiving this mail because:
You are the assignee for the bug.