Currently Linux 2.6 assumes the BIOS (or firmware) sets the master abort 
mode flag on PCI bridge chips in a coherent fashion.  This is not always 
the case and the consequences of getting this flag incorrect can cause 
hardware to fail or silent data corruption.  This patch lets the user 
override the BIOS master abort setting at boot time and the distro 
maintainer to set a default according to their target audience.

The comments in the patch are probably a bit too verbose, but I think it 
is a good patch to start discussions around.  If it is decided that 
something should be done about this problem, this patch could be 
included in a -mm release and migrate into Linus's kernel as appropriate.

This incarnation of the patch has had minimal testing.  For our internal 
kernels, we always force the master abort mode to 1 and then let the 
device drivers for hardware we know can't handle target aborts switch 
the master abort mode to 0. This does not seem appropriate for general 
release.

Some background for those who do not spend most of their waking hours 
exploring buses and what can go wrong.

The master abort flag tells a PCI bridge what to do when a bus master 
behind the bridge requests the bus and the bridge is unable to get the 
bus.  With the flag clear, for master reads the bridge returns all 
0xff's (hence silent data corruption) and for master writes, it throws 
the data away.  With the bit set, the bridge sends a target abort to the 
master.  This can only happen when the system is heavily loaded.

The problem with always setting the bit is that some PCI hardware, 
notably some Intel E-1000 chips (Ethernet controller: Intel Corporation: 
Unknown device 1076) cannot properly handle the target abort bit.  In 
the case of the E-1000 chip, the driver must reset the chip to recover. 
This usually leads to the machine being off the network for several 
seconds, or sometimes even minutes, which can be bad for servers.

I even have a single motherboard with both a device that cannot handle 
the target abort and an IDE controller that can handle the target abort 
behind the same bridge.  For this motherboard, I have to choose the 
lesser of two evils, network hiccups or potential data corruption.
For the record, I have seen both occur.  Other people may make wish to 
make a different choice than we did, hence this patch allows the user to 
choose the mode at runtime.

	Ross