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Andi Kleen (ak@muc.de) wrote : > AMD has published a new errata sheet for the AMD762, which describes > the root cause of the infamous "AMD 762 unstable when no PS/2 mouse > connected" bug. The reason is that without a PS/2 mouse the BIOS doesn't > put a data page in front of the VGA buffer at 640K. When the kernel > puts a page cache page there and does busmaster IO with it then the automatic > PCI prefetch from the chipset can hit the VGA buffer and that may cause a hang. > > > The workaround is to reserve the page directly before 640K if it wasn't > already reserved by the BIOS. > > > The bug only occurs in newer revisions (B0,B1) > > > The workaround here is somewhat hackish. We can only reserve the page > in early boot, but at that time there is no easy way to check for the > AMD762's PCI-ID because the PCI subsystem hasn't been initialized yet. > > > This patch checks later during the pci quirks pass instead > and then tells the user to pass a kernel option - "vgaguard" - in > case of instability. This is not ideal, but probably preferable than > to connect PS/2 mouses to all boxes in a colocated rack. Another > way would be to always reserve that page, but I didn't feel like > punishing everybody just for a hardware bug in a single chipset. > > > Patch for 2.5.53. Please consider applying. Some suggestions : - do not tell the user to use the "vgaguard" option if he is already using it - change to more informative text : old : I/O APIC: AMD762 Errata #56 may be present. In case of instability boot with "vgaguard" or connect a PS/2 mouse. new: I/O APIC: AMD762 Errata #56 may be present. In case of instability boot with the "vgaguard" kernel boot option or connect a PS/2 mouse and reboot. Just connecting a PS/2 mouse on a running system does not help, right ? :-) - maybe rename the option to "amd762vgaguard" ? - also write some docs and put a link to it in the kernel message ? For now this would be enough : I/O APIC: AMD762 Errata #56 may be present. In case of instability boot with the "vgaguard" kernel boot option or connect a PS/2 mouse and reboot. See http://www.uwsg.indiana.edu/hypermail/linux/kernel/0212.3/0043.html Regards, David Balazic - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | |||||||||
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