James Bottomley wrote: > On Mon, 2005-12-12 at 15:00 -0600, Michael Reed wrote: >>(The subject of this email isn't quite accurate. It's not >>a pci coherency problem, it's a pio write ordering problem.) >> >>I've been asked to pass along the suggestion that "mmiowb" >>should be implemented for the platform. > >>Given that I've been unable to unearth the chipset documentation >>for the Vis WS, I can only hope that you've got some good ideas >>on how this might be accomplished. > > Well, the idea was that mmiowb and posting flushes were orthogonal. > mmiowb would be used in places where a posted write flush was done but > was strictly unnnecessary. This bug report is implying that the posted > write flush was necessary, so it was incorrectly replaced with mmiowb > (which is a nop on most platforms). The mmiowb() is sufficient to assure ordering of the write to the board register. (Have I incorrectly used the term pio? I'm not meaning to imply a particular address space used to access a board's registers.) It's not a timing issue. The WRT_REG write doesn't have to reach the board before the driver can perform another function. It just has to reach the board in the order issued. > >>I agree that replacing the pio read which flushed the preceeding >>pio write with mmiowb() is what has likely broken the driver. If you >>restore them, please make it either mmiowb or pio read, but not both. >> >>Perhaps something like this? It's not the most elegant solution.... > > I'm tempted to say I think we need to put the write posting flush back > in and dump the mmiowb(), but since the driver is supposedly doing PIO > for VISWS, there's something else going on here (PIO writes aren't > supposed to post). I've cc'd the VISWS maintainer in case he can think > of anything. Again, apologies if I've misused the term PIO. Mike > > James > > > - > : send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > > - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
