Messages in this thread Patch in this message | | | Date | Fri, 07 Nov 2008 00:23:41 -0500 | From | Mathieu Desnoyers <> | Subject | [RFC patch 05/18] get_cycles() : MIPS HAVE_GET_CYCLES_32 |
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partly reverts commit efb9ca08b5a2374b29938cdcab417ce4feb14b54. Selects HAVE_GET_CYCLES_32 only on CPUs where it is safe to use it.
Currently consider the "_WORKAROUND" cases for 4000 and 4400 to be unsafe, but should probably add other sub-architecture to the blacklist.
Do not define HAVE_GET_CYCLES because MIPS does not provide 64-bit tsc (only 32-bits).
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> CC: Ralf Baechle <ralf@linux-mips.org> CC: David Miller <davem@davemloft.net> CC: Linus Torvalds <torvalds@linux-foundation.org> CC: Andrew Morton <akpm@linux-foundation.org> CC: Ingo Molnar <mingo@redhat.com> CC: Peter Zijlstra <a.p.zijlstra@chello.nl> CC: Thomas Gleixner <tglx@linutronix.de> CC: Steven Rostedt <rostedt@goodmis.org> CC: linux-arch@vger.kernel.org --- arch/mips/Kconfig | 4 ++++ arch/mips/include/asm/timex.h | 25 +++++++++++++++++++++++++ 2 files changed, 29 insertions(+)
Index: linux.trees.git/arch/mips/include/asm/timex.h =================================================================== --- linux.trees.git.orig/arch/mips/include/asm/timex.h 2008-10-30 20:22:50.000000000 -0400 +++ linux.trees.git/arch/mips/include/asm/timex.h 2008-11-07 00:10:10.000000000 -0500 @@ -29,14 +29,39 @@ * which isn't an evil thing. * * We know that all SMP capable CPUs have cycle counters. + * + * Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> + * HAVE_GET_CYCLES makes sure that this case is handled properly : + * + * Ralf Baechle <ralf@linux-mips.org> : + * This avoids us executing an mfc0 c0_count instruction on processors which + * don't have but also on certain R4000 and R4400 versions where reading from + * the count register just in the very moment when its value equals c0_compare + * will result in the timer interrupt getting lost. */ typedef unsigned int cycles_t; +#ifdef HAVE_GET_CYCLES_32 +static inline cycles_t get_cycles(void) +{ + return read_c0_count(); +} + +static inline void get_cycles_barrier(void) +{ +} + +static inline cycles_t get_cycles_rate(void) +{ + return CLOCK_TICK_RATE; +} +#else static inline cycles_t get_cycles(void) { return 0; } +#endif #endif /* __KERNEL__ */ Index: linux.trees.git/arch/mips/Kconfig =================================================================== --- linux.trees.git.orig/arch/mips/Kconfig 2008-11-07 00:06:06.000000000 -0500 +++ linux.trees.git/arch/mips/Kconfig 2008-11-07 00:10:10.000000000 -0500 @@ -1611,6 +1611,10 @@ config CPU_R4000_WORKAROUNDS config CPU_R4400_WORKAROUNDS bool +config HAVE_GET_CYCLES_32 + def_bool y + depends on !CPU_R4400_WORKAROUNDS + # # Use the generic interrupt handling code in kernel/irq/: # -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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