On Wed, Apr 06, 2005 at 05:22:57PM +0200, Joakim Tjernlund wrote: > All cache instructions in 8xx are somewhat buggy as they > do not update the DAR register when causing a DTLB Miss/Error [snip] > ===== head_8xx.S 1.21 vs edited ===== [snip] > +#define CONFIG_8xx_DCBxFIXED
If this is configurable, it needs to be done in the Kconfig like, well a real config option. The arguement for doing it as a config option is that it is possible to avoid these instructions in userland (I _think_ with a properly configured gcc, all you need to do is remove the memset.S file from glibc), and avoid the (theoretical) slow-down. That said, it should also probably be an 'advanced' option that defaults to the fixup. [snip] > +#ifdef CONFIG_8xx_DCBxFIXED > +/* These macros are used to tag DAR with a known value so that the > + * DataTLBError can recognize a buggy dcbx instruction and workaround > + * the problem. > + */ > +#define TAG_VAL 0x00f0 /* -1 may also be used */ Is there an advantage of using -1? If it just "or we could use", perhaps we should just comment about it, and always define TAG_VAL to 0x00f0 (which will make the rest of the patch a bit cleaner). [snip] > +#ifdef CONFIG_8xx_DCBxFIXED > +/* This is the workaround procedure to calculate the data EA for buggy > dcbx,dcbi instructions > + * by decoding the registers used by the dcbx instruction and adding them. > + * DAR is set to the calculated address and r10 also holds the EA on exit. > + */ > +//#define INSTR_CHECK /* define to verify if it is a dcbx instr. Should not > be needed. */ > +//#define NO_SELF_MODIFYING_CODE /* define if you don't want to use self > modifying code */ > +//#define DEBUG_DCBX_INSTRUCTIONS /* for debugging only. Needs INSTR_CHECK > defined as well. */ > +//#define KERNEL_SPACE_ONLY /* define if user space do NOT contain dcbx > instructions. */ Aside from preferring #undef FOO to /* #define FOO *//* Comment */ and detesting // comments: - Perhaps just one debug symbol (combine INSTR_CHECK and DEBUG_DCBX_INSTRUCTIONS). - Is there (aside from "eww, self modifying code") a good reason to have NO_SELF_MODIFYING_CODE ? - Since today, IIRC, we avoid these instructions in the kernel anyhow, is there a reason for KERNEL_SPACE_ONLY ? In my mind at least, I could see a why for userspace-only, but would think an all/nothing approach is probably most sane (if you can avoid in space A why not B?). -- Tom Rini http://gate.crashing.org/~trini/
