On 4/2/24 08:29, Sven Schnelle wrote:
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.
This is how it works on real physical hardware, and since qemu should mimic
real hardware as best as it can, IMHO we should implement it exactly like this.
Helge
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/
