[PATCH] [ARM] Add ARCH_PROVIDES_UDELAY config option

[Colin Cross]

The discussion took place on lkml and the cpufreq lists.  See
http://lkml.org/lkml/2010/4/23/323

I reposted the patch with a revised commit message addressing
Saravana's comments.

On Fri, Apr 30, 2010 at 3:12 AM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> 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)
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel at lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>