On Mon, Apr 25, 2022 at 9:39 AM Maciej W. Rozycki macro@orcam.me.uk wrote:
Fix the discrepancy between the two places we check for the CP0 counter erratum in along with the incorrect comparison of the R4400 revision number against 0x30 which matches none and consistently consider all R4000 and R4400 processors affected, as documented in processor errata publications[1][2][3], following the mapping between CP0 PRId register values and processor models:
PRId | Processor Model ---------+-------------------- 00000422 | R4000 Revision 2.2 00000430 | R4000 Revision 3.0 00000440 | R4400 Revision 1.0 00000450 | R4400 Revision 2.0 00000460 | R4400 Revision 3.0
No other revision of either processor has ever been spotted.
Contrary to what has been stated in commit ce202cbb9e0b ("[MIPS] Assume R4000/R4400 newer than 3.0 don't have the mfc0 count bug") marking the CP0 counter as buggy does not preclude it from being used as either a clock event or a clock source device. It just cannot be used as both at a time, because in that case clock event interrupts will be occasionally lost, and the use as a clock event device takes precedence.
Compare against 0x4ff in `can_use_mips_counter' so that a single machine instruction is produced.
References:
[1] "MIPS R4000PC/SC Errata, Processor Revision 2.2 and 3.0", MIPS Technologies Inc., May 10, 1994, Erratum 53, p.13
[2] "MIPS R4400PC/SC Errata, Processor Revision 1.0", MIPS Technologies Inc., February 9, 1994, Erratum 21, p.4
[3] "MIPS R4400PC/SC Errata, Processor Revision 2.0 & 3.0", MIPS Technologies Inc., January 24, 1995, Erratum 14, p.3
Signed-off-by: Maciej W. Rozycki macro@orcam.me.uk Fixes: ce202cbb9e0b ("[MIPS] Assume R4000/R4400 newer than 3.0 don't have the mfc0 count bug") Cc: stable@vger.kernel.org # v2.6.24+
arch/mips/include/asm/timex.h | 8 ++++---- arch/mips/kernel/time.c | 11 +++-------- 2 files changed, 7 insertions(+), 12 deletions(-)
Reviewed-by: Philippe Mathieu-Daudé f4bug@amsat.org