Richard Henderson <richard.hender...@linaro.org> writes: > On 4/1/24 20:01, Sven Schnelle wrote: >> Implement dr2 and the mfdiag/mtdiag instructions. dr2 contains a bit >> which enables/disables space id hashing. Seabios would then set >> this bit when booting. Linux would disable it again during boot (this >> would be the same like on real hardware), while HP-UX would leave it >> enabled. > > Pointer to documentation?
There's no documentation about that in the public. There's this code since the beginning of linux on hppa in the linux kernel (arch/parisc/kernel/pacache.S): /* Disable Space Register Hashing for PCXL */ .word 0x141c0600 /* mfdiag %dr0, %r28 */ depwi 0,28,2, %r28 /* Clear DHASH_EN & IHASH_EN */ .word 0x141c0240 /* mtdiag %r28, %dr0 */ b,n srdis_done srdis_pa20: /* Disable Space Register Hashing for PCXU,PCXU+,PCXW,PCXW+,PCXW2 */ .word 0x144008bc /* mfdiag %dr2, %r28 */ depdi 0, 54,1, %r28 /* clear DIAG_SPHASH_ENAB (bit 54) */ .word 0x145c1840 /* mtdiag %r28, %dr2 */ So PCXL (32 bit) uses dr0, while 64 bit uses dr2. This still is the same on my C8000 - i see firmware still contains code reading dr2 to figure out whether space id hashing is enabled. The mfdiag/mtdiag instructions are described in the PCXL/PCXL2 ERS. https://parisc.wiki.kernel.org/index.php/File:PCXL_ers.pdf https://parisc.wiki.kernel.org/index.php/File:Pcxl2_ers.pdf There was a discussion mentioning disabling Space ID hashing in Linux: https://yhbt.net/lore/linux-parisc/199912161642.iaa11...@lucy.cup.hp.com/
