svn commit: r266083 - in head/sys/arm: arm include

[Michael Tuexen]

On 24 May 2014, at 23:02, Andrew Turner <andrew at fubar.geek.nz> wrote:

> On Sat, 24 May 2014 21:09:56 +0200
> Michael Tuexen <tuexen at freebsd.org> wrote:
> 
>> On 22 May 2014, at 09:09, Mark R V Murray <markm at FreeBSD.org> wrote:
>> 
>>> 
>>> On 21 May 2014, at 21:15, Hans Petter Selasky <hps at selasky.org>
>>> wrote:
>>> 
>>>> On 05/14/14 21:11, Mark Murray wrote:
>>>>> Author: markm
>>>>> Date: Wed May 14 19:11:15 2014
>>>>> New Revision: 266083
>>>>> URL: http://svnweb.freebsd.org/changeset/base/266083
>>>>> 
>>>>> Log:
>>>>> Give suitably-endowed ARMs a register similar to the x86 TSC
>>>>> register.
>>>>> 
>>>> 
>>>> Hi,
>>>> 
>>>> Regression issue:
>>>> This commit prevents RPI-B from booting.
>>> 
>>> Thanks, I’ll look at it ASAP.
>> Doesn't the ARM1176 use for example
>> MRC p15, 0, <Rd>, c15, c12, 1    ; Read Cycle Counter Register
>> to read the value, whereas the 
>> you use 
>> __asm __volatile("mrc p15, 0, %0, c9, c13, 0": "=r" (ccnt));
> 
> On ARMv6 there is no guarantee of a cycle count register. On the
> ARM1176 there is one in an implementation defined section of the system
> control coprocessor. This is the c15 section above, and is accessible
> as shown.
> 
> On ARMv7 there are optional performance monitor extensions. These are
> in parts of the c9 section of the coprocessor. As it is optional there
> is no requirement for implementers to include this functionality,
> however I would expect the ARM designs to include it, and most non-ARM
> designs are likely aiming for performance so will also include them.
> 
> If the ARMv7 processor has the performance extensions the existing code
> appears correct to retrieve it.
The code is #ifdef as

#if defined(CPU_ARM1136) || defined(CPU_ARM1176) \
  || defined(CPU_MV_PJ4B) \
  || defined(CPU_CORTEXA) || defined(CPU_KRAIT)

Isn't the Raspberry Pi defining CPU_ARM1176 and using ARMv6? So can we use
the same code for all plattforms in the #ifdef?

Best regards
Michael
> 
> Andrew
> 
>