From: David Woodhouse <dw...@infradead.org>
Date: Mon, 19 Feb 2018 15:24:18 +0000
>> For one, the sparc specific code allows mmap'ing any address range
>> within a PCI bus device. The generic code does not allow that.
> You mean any address range in a given PCI bus even if there is no
> actual device with a BAR at the corresponding address?
> Would I be right to assume this was only available through the legacy
> procfs API? I think it should be possible to accommodate it, and it
> does look like I'd missed this requirement the first time round; thanks
> for pointing it out.
It was probably the case that only procfs could do it.
It is the mechanism by which we were able to let the X server poke
around in VGA ISA space. It does a bus I/O space map for the bus
device above the VGA card.