Loic Prylli wrote:
I just realized one thing: the bar sizing code in pci_read_bases() (that
writes 0xffffffff in the bars) does not seem to disable the
PCI_COMMAND_MEM/PCI_COMMAND_IO bits in the cmd register before
manipulating the BARs. And it seems nobody else ensures they are
disabled at this point either (or am I missing something?).
No you're not missing anything. This problem causes many machines to
break horribly when MMCONFIG is enabled. There's a patch in -mm to fix
this. (It special-cases the case of host bridges and doesn't disable the
decode bits for those, since some are known to do crazy things if you
do that.)
http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.24-rc6/2.6.24-rc6-mm1/broken-out/pci-disable-decoding-during-sizing-of-bars.patch
Touching the bars while they are enabled would be buggy behaviour from
our part, and something trivial to fix. And it might well fix that
particular problem (it's fair play from the machine to crash if we
create a decoding conflict, simply disabling the cmd bits in
pci_read_bases() should remove that conflict).
FWIW, to partially answer your last question, Windows does disable
mem-space and/or IO-space when sizing the bars of a device (I have some
traces of configuration-space-access taken on a window machine for one
of the PCI busses).
Good to know. There was some speculation that it did not.
--
Robert Hancock Saskatoon, SK, Canada
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Home Page: http://www.roberthancock.com/
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