accessing a PCIe register from userspace through kmem or other ways ?

[Ryan Stone]

On Mon, Apr 4, 2016 at 6:45 PM, John Baldwin <jhb at freebsd.org> wrote:

> I suspect Ryan might be referring to BARs outside of the DMAP which we
> only populate to Maxmem IIRC.  /dev/mem should work for those.
>

Unfortunately I no longer have access to the systems so I can't really
confirm.  I had a debug tool that attempted to read PCI device registers
through /dev/mem, and on these systems (which were running a 8.2
derivative) the reads from /dev/mem failed with some kind of error.

The one detail that I do remember is that the errors started happening
after we enabled the use of 64-bit BARs in the BIOS and the addresses
assigned to the BARs were quite large -- I believe well beyond the bounds
of real memory.