[PATCH 5/5] arm/perfevents: implement perf event support for ARMv6

[Tomasz Fujak]

Where do I find a repository that contains the latest performance events/ARM
efforts?


> -----Original Message-----
> From: linux-arm-kernel-bounces at lists.infradead.org [mailto:linux-arm-
> kernel-bounces at lists.infradead.org] On Behalf Of Jean Pihet
> Sent: Thursday, January 21, 2010 1:22 PM
> To: Russell King - ARM Linux
> Cc: 'Jamie Iles'; Will Deacon; linux-arm-kernel at lists.infradead.org
> Subject: Re: [PATCH 5/5] arm/perfevents: implement perf event support
> for ARMv6
> 
> On Thursday 21 January 2010 11:38:03 Russell King - ARM Linux wrote:
> > On Thu, Jan 21, 2010 at 10:28:26AM -0000, Will Deacon wrote:
> > > Hi Jamie,
> > >
> > > * Jamie Iles wrote:
> > > > Given the difficulty in determining the CPU type 100%, this
> should be
> > > > changed to:
> > > >
> > > > 	unsigned long cpuid = read_cpuid_id();
> > > > 	unsigned long implementor = (cpuid & 0xFF000000) >> 24;
> > > > 	unsigned long part_number = (cpuid & 0xFFF0);
> > > >
> > > > 	/* We only support ARM CPUs implemented by ARM at the
> moment. */
> > > > 	if (implementor == 0x41) {
> > > > 		switch (part_number) {
> > > > 		case 0xB360:
> > > > 		case 0xB560:
> > > > 			etc
> > >
> > > Whilst I understand that the whole cpuid thing is a complete mess
> [I saw
> > > the lkml posts yesterday], I'm not sure this is necessary for v7
> cores.
> > > For v7, the PMU is part of the architecture and so *must* be
> implemented
> > > in the way described in the ARM ARM [Chapter 9], regardless of the
> > > implementer.
> >
> > This function is called whenever the PMU support is built in - and
> > this is the first place a decision is made about how to handle stuff.
> >
> > Merely checking the part number without checking the implementer is
> > nonsense - the part number is defined by the implmenter, not ARM, so
> > the part number can only be interpreted with knowledge of the
> > implementer.
> >
> > So, when v7 gets added, checking the main ID register is the wrong
> > thing to do.
> >
> > Given that cpu_architecture() appears to have been redefined to
> return
> > the MMU architecture, we have no real way to properly determine if we
> > have a v7 PMU present - in fact, the whole "are we v6 or v7 or
> something
> > later" question seems to be extremely muddy and indeterminant.
> >
> > So I don't think even checking cpu_architecture() == CPU_ARCH_ARMv7
> > is the right thing either.
> Agree. Here is the latest version of the detection code, after merging
> Jamie's
> latest version:
> 
>         unsigned long cpuid = read_cpuid_id() & CPUID_MASK;
> 
>         switch (cpuid) {
>         case 0xB360:    /* ARM1136 */
>         case 0xB560:    /* ARM1156 */
>         case 0xB760:    /* ARM1176 */
> 	    ...
>                 break;
>         case 0xB020:    /* ARM11mpcore */
> 	    ...
>                 break;
>         case 0xC080:    /* Cortex-A8 */
> 	    ...
>                 break;
>         case 0xC090:    /* Cortex-A9 */
> 	    ...
>                 break;
>         default:
>                 pr_info("no hardware support available\n");
>                 perf_max_events = -1;
>        }
>        ...
> 
> Is that OK if we just add 'if (implementor == 0x41) {' before the
> switch
> statement, as proposed above?
> 
> Jean
> 
> 
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