On Thu, 2009-10-08 at 17:36 -0700, Dan Malek wrote: > On Oct 8, 2009, at 3:23 PM, Benjamin Herrenschmidt wrote: > > > << > > • Reference and change bit updates—The MPC850 does not generate an > > exception for > > an R (reference) bit update. In fact, there is no entry for an R > > bit in the TLB. > > The change bit (C) is bit 23 in the level-two descriptor, > > described in Table 8-4. > > Software updates C (changed) bits, but hardware treats the C bit > > (negated) as a > > write-protect attribute. Therefore, attempting to write to a page > > marked unmodified > > invalidates that entry and causes an implementation-specific DTLB > > error exception. > > ^^^^^^^^^^^^^^^^^^^^^^ > > If change bits are not needed, set the C bit to one by default in > > the PTEs. > > How interesting.... > > I've looked at many 8xx docs and they all have the same text > (probably cut/paste :-)) I'd place some debug code in the C functions > to print out a few of the TLB Entry for various errors to see if this > really > happens, and for other errors, too. I guess I never stumbled into > this because I always thought I had to do everything from software, > so just made sure I did.
I'm not sure it's worth bothering :-) I'm happy to continue assuming we need to tlbie and always make sure we do so. Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
