[PATCH] [ARM] Add ARCH_PROVIDES_UDELAY config option

[Russell King - ARM Linux]

Please re-post the entire series/thread; because the list server has
a very short timeout on delivery of mail, I don't have anything that
was discussed during the last week.

On Thu, Apr 29, 2010 at 07:51:02PM -0700, Saravana Kannan wrote:
> You beat me to it :-) I was thinking of doing this for now before trying  
> to find the *perfect* fix with the cpufreq maintainers.
>
> If you want, you can also add in details about how using a constant freq  
> counter would also avoid the issue of CPU freq switching while we are  
> delay looping.
>
> The current ARM implementation doesn't handle this either.
>
> If my opinion matters, I think this is a good patch.
>
> -Saravana
>
> Colin Cross wrote:
>> On SMP kernels, the loops_per_jiffy value is not scaled, leading to
>> udelays that are too long if the CPU frequency is scaled down from
>> the frequency at loops_per_jiffy calibration, or too short if the
>> frequency is scaled up.  Some SOCs have a timer with a constant tick
>> rate that can be used to time udelays, similar to the TSC on x86.
>> Provide a config flag to allow these SOCs to override the default
>> ARM udelay implementation.
>>
>> Signed-off-by: Colin Cross <ccross at android.com>
>> ---
>>  arch/arm/Kconfig             |    3 +++
>>  arch/arm/include/asm/delay.h |    4 ++++
>>  arch/arm/lib/Makefile        |    6 +++++-
>>  3 files changed, 12 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>> index 33d2825..d9923b0 100644
>> --- a/arch/arm/Kconfig
>> +++ b/arch/arm/Kconfig
>> @@ -175,6 +175,9 @@ config ARM_L1_CACHE_SHIFT_6
>>  	help
>>  	  Setting ARM L1 cache line size to 64 Bytes.
>>  +config ARCH_PROVIDES_UDELAY
>> +  bool
>> +
>>  if OPROFILE
>>   config OPROFILE_ARMV6
>> diff --git a/arch/arm/include/asm/delay.h b/arch/arm/include/asm/delay.h
>> index b2deda1..57f1fa0 100644
>> --- a/arch/arm/include/asm/delay.h
>> +++ b/arch/arm/include/asm/delay.h
>> @@ -8,6 +8,9 @@
>>   #include <asm/param.h>	/* HZ */
>>  +#ifdef CONFIG_ARCH_PROVIDES_UDELAY
>> +#include <mach/delay.h>
>> +#else
>>  extern void __delay(int loops);
>>   /*
>> @@ -40,5 +43,6 @@ extern void __const_udelay(unsigned long);
>>  			__const_udelay((n) * ((2199023U*HZ)>>11))) :	\
>>  	  __udelay(n))
>>  +#endif /* defined(ARCH_PROVIDES_UDELAY) */
>>  #endif /* defined(_ARM_DELAY_H) */
>>  diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
>> index 030ba72..aa449e3 100644
>> --- a/arch/arm/lib/Makefile
>> +++ b/arch/arm/lib/Makefile
>> @@ -6,7 +6,7 @@
>>   lib-y		:= backtrace.o changebit.o csumipv6.o csumpartial.o   \
>>  		   csumpartialcopy.o csumpartialcopyuser.o clearbit.o \
>> -		   delay.o findbit.o memchr.o memcpy.o		      \
>> +		   findbit.o memchr.o memcpy.o                        \
>>  		   memmove.o memset.o memzero.o setbit.o              \
>>  		   strncpy_from_user.o strnlen_user.o                 \
>>  		   strchr.o strrchr.o                                 \
>> @@ -17,6 +17,10 @@ lib-y		:= backtrace.o changebit.o csumipv6.o csumpartial.o   \
>>   mmu-y	:= clear_user.o copy_page.o getuser.o putuser.o
>>  +ifneq ($(CONFIG_ARCH_PROVIDES_UDELAY),y)
>> +  lib-y += delay.o
>> +endif
>> +
>>  # the code in uaccess.S is not preemption safe and
>>  # probably faster on ARMv3 only
>>  ifeq ($(CONFIG_PREEMPT),y)
>
>
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