Messages in this thread | ![/](/images/icornerl.gif) | | From | Philippe Mathieu-Daudé <> | Date | Fri, 29 Apr 2022 15:04:07 +0200 | Subject | Re: [PATCH] MIPS: Fix CP0 counter erratum detection for R4k CPUs |
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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>
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