[PATCH:libpciaccess 3/3] Support more pci functions on NetBSD.

[Matthieu Herrb]

On Fri, Jun 14, 2013 at 12:54:43PM +0200, Thomas Klausner wrote:
> Hi Matthieu!
> > > +#elif defined(PCI_MAGIC_IO_RANGE)
> > > +	ret->memory = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED,
> > > +	    aperturefd, PCI_MAGIC_IO_RANGE + base);
> > 
> > Hmm where is aperturefd defined in the NetBSD case ? (I know it's is
> > defined as static in  openbsd_pci.c, but I can't find the similar hack
> > for NetBSD
> 
> That's a copy'n'paste error from openbsd_pci.c. PCI_MAGIC_IO_RANGE is
> only defined for a few ports of NetBSD anyway, and neither me nor
> Chuck know what the proper way to do this is. I guess I'll just remove
> this #elif clause.

The idea behind PCI_MAGIC_IO_RANGE is to define a particular vm
address where the kernel would map the I/O range of the card, so that
inb/outb style functions in userland can access them, when the driver
has no knowledge of explicit MMIO mappings. 

IIRC in NetBSD Michael Lorenz has fixed a number of drivers to do
explicit MMIO in order to avoid the need for that hack.

> 
> > -- and it should not be needed in NetBSD's case where all
> > memory can be be mapped through the /dev/pci* entry).
> 
> Can you please expand on this or suggest what the patch should look
> like?
> 

On OpenBSD we have  the "aperture driver" which provides
access to device memory through /dev/xf86 (instead of /dev/mem or the
console device) and privilege separation in the X server.

'aperturefd' in openbsd_pci.c is a separate static variable holding
the file descriptor for /dev/xf86, and is initialized by
pci_system_init_dev_mem(), an OpenBSD specific libpciaccess function
that is called early, while the X server still has root privileges,
before calling pci_system_init().

On NetBSD you don't have that extra device to open and that extra file
descriptor to keep, since the xserver is running as root and can open
the /dev/pci* devices at will. So even  in the PCI_MAGIG_IO_RANGE, you
should use either the file descriptor for the current PCI bus or open
/dev/mem explicitely in that mmap() call.

While moving to KMS this is probably an area where we can clean up
things and simplify them on OpenBSD, but for now we decided to get KMS
working with minimal changes only.
-- 
Matthieu Herrb