From: Maciej W. Rozycki macro@orcam.me.uk
commit f0a6c68f69981214cb7858738dd2bc81475111f7 upstream.
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.
[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+ Reviewed-by: Philippe Mathieu-Daudé f4bug@amsat.org Signed-off-by: Thomas Bogendoerfer tsbogend@alpha.franken.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/mips/include/asm/timex.h | 8 ++++---- arch/mips/kernel/time.c | 11 +++-------- 2 files changed, 7 insertions(+), 12 deletions(-)
--- a/arch/mips/include/asm/timex.h +++ b/arch/mips/include/asm/timex.h @@ -40,9 +40,9 @@ typedef unsigned int cycles_t;
/* - * On R4000/R4400 before version 5.0 an erratum exists such that if the - * cycle counter is read in the exact moment that it is matching the - * compare register, no interrupt will be generated. + * On R4000/R4400 an erratum exists such that if the cycle counter is + * read in the exact moment that it is matching the compare register, + * no interrupt will be generated. * * There is a suggested workaround and also the erratum can't strike if * the compare interrupt isn't being used as the clock source device. @@ -63,7 +63,7 @@ static inline int can_use_mips_counter(u if (!__builtin_constant_p(cpu_has_counter)) asm volatile("" : "=m" (cpu_data[0].options)); if (likely(cpu_has_counter && - prid >= (PRID_IMP_R4000 | PRID_REV_ENCODE_44(5, 0)))) + prid > (PRID_IMP_R4000 | PRID_REV_ENCODE_44(15, 15)))) return 1; else return 0; --- a/arch/mips/kernel/time.c +++ b/arch/mips/kernel/time.c @@ -140,15 +140,10 @@ static __init int cpu_has_mfc0_count_bug case CPU_R4400MC: /* * The published errata for the R4400 up to 3.0 say the CPU - * has the mfc0 from count bug. + * has the mfc0 from count bug. This seems the last version + * produced. */ - if ((current_cpu_data.processor_id & 0xff) <= 0x30) - return 1; - - /* - * we assume newer revisions are ok - */ - return 0; + return 1; }
return 0;