[v2 3/9] ARM: tegra: # of CPU cores detection w/ & w/o HAVE_ARM_SCU

[Hiroshi Doyu]

Lorenzo Pieralisi <lorenzo.pieralisi at arm.com> wrote @ Thu, 10 Jan 2013 14:47:23 +0100:

> On Thu, Jan 10, 2013 at 12:58:13PM +0000, Hiroshi Doyu wrote:
> > Lorenzo Pieralisi <lorenzo.pieralisi at arm.com> wrote @ Wed, 9 Jan 2013 16:17:00 +0100:
> > 
> > ....
> > 
> > > > diff --git a/arch/arm/mach-tegra/platsmp.c b/arch/arm/mach-tegra/platsmp.c
> > > > index 68e76ef..51d24ae 100644
> > > > --- a/arch/arm/mach-tegra/platsmp.c
> > > > +++ b/arch/arm/mach-tegra/platsmp.c
> > > > @@ -152,7 +152,7 @@ done:
> > > >   * Initialise the CPU possible map early - this describes the CPUs
> > > >   * which may be present or become present in the system.
> > > >   */
> > > > -static void __init tegra_smp_init_cpus(void)
> > > > +static void __init tegra_smp_detect_cores(void)
> > > >  {
> > > >  	unsigned int i, cpu_id, ncores;
> > > >  	u32 l2ctlr;
> > > > @@ -183,6 +183,12 @@ static void __init tegra_smp_init_cpus(void)
> > > >  
> > > >  	for (i = 0; i < ncores; i++)
> > > >  		set_cpu_possible(i, true);
> > > > +}
> > > > +
> > > > +static void __init tegra_smp_init_cpus(void)
> > > > +{
> > > > +	if (!num_possible_cpus())
> > > > +		tegra_smp_detect_cores();
> > > 
> > > Thought about this, I would prefer writing an inline function that
> > > provides this information (DT missing /cpu information or parsing failure)
> > > instead of relying on num_possible_cpus to be == 0 as a way to check that.
> > 
> > With your "[PATCH] ARM: kernel: DT cpu map validity check helper
> > function", my original patch gets as below. I think that the following
> > "smp_detect_ncores()" function may be so generic that it could be
> > moved in some common place than platform?
> 
> Possibly, but I have still some comments to add.
> 
> > 
> > From f5f2a43952ce75fe061b3808b994c3ceb07f1af1 Mon Sep 17 00:00:00 2001
> > From: Hiroshi Doyu <hdoyu at nvidia.com>
> > Date: Mon, 26 Nov 2012 12:25:14 +0200
> > Subject: [PATCH 1/1] ARM: tegra: # of CPU cores detection w/ & w/o
> >  HAVE_ARM_SCU
> > 
> > The method to detect the number of CPU cores on Cortex-A9 MPCore and
> > Cortex-A15 MPCore is different. On Cortex-A9 MPCore we can get this
> > information from the Snoop Control Unit(SCU). On Cortex-A15 MPCore we
> > have to read it from the system coprocessor(CP15), because the SCU on
> > Cortex-A15 MPCore does not have software readable registers. This
> > patch selects the correct method at runtime based on the CPU ID.
> > 
> > Signed-off-by: Hiroshi Doyu <hdoyu at nvidia.com>
> > ---
> >  arch/arm/mach-tegra/platsmp.c |   54 ++++++++++++++++++++++++++++++++---------
> >  1 file changed, 43 insertions(+), 11 deletions(-)
> > 
> > diff --git a/arch/arm/mach-tegra/platsmp.c b/arch/arm/mach-tegra/platsmp.c
> > index 6867030..9a1324a 100644
> > --- a/arch/arm/mach-tegra/platsmp.c
> > +++ b/arch/arm/mach-tegra/platsmp.c
> > @@ -24,6 +24,8 @@
> >  #include <asm/mach-types.h>
> >  #include <asm/smp_scu.h>
> >  #include <asm/smp_plat.h>
> > +#include <asm/cputype.h>
> > +#include <asm/prom.h>
> >  
> >  #include <mach/powergate.h>
> >  
> > @@ -38,7 +40,7 @@
> >  extern void tegra_secondary_startup(void);
> >  
> >  static cpumask_t tegra_cpu_init_mask;
> > -static void __iomem *scu_base = IO_ADDRESS(TEGRA_ARM_PERIF_BASE);
> > +static void __iomem *scu_base;
> >  
> >  #define EVP_CPU_RESET_VECTOR \
> >  	(IO_ADDRESS(TEGRA_EXCEPTION_VECTORS_BASE) + 0x100)
> > @@ -177,23 +179,52 @@ done:
> >  	return status;
> >  }
> >  
> > +static int __init smp_detect_ncores(void)
> > +{
> > +	unsigned int ncores, mpidr;
> > +	u32 l2ctlr;
> > +	phys_addr_t pa;
> > +
> > +	mpidr = read_cpuid_mpidr();
> > +	switch (mpidr) {
> > +	case ARM_CPU_PART_CORTEX_A15:
> > +		asm("mrc p15, 1, %0, c9, c0, 2\n" : "=r" (l2ctlr));
> > +		ncores = ((l2ctlr >> 24) & 3) + 1;
> > +		break;
> 
> I do not want to see the case above merged. We keep the existing legacy
> methods there for legacy reasons and as a fall-back mechanism but I am not
> keen on adding new HW probing code to detect the number of cores.
> 
> From A15/A7 onwards DT-only cpu map initialization is the way to go.

Ok, then, smp_detect_ncores(void) could be...

static int __init smp_detect_ncores(void)
{
	unsigned int ncores, mpidr;
	phys_addr_t pa;

	mpidr = read_cpuid_mpidr();
	switch (mpidr) {
	case ARM_CPU_PART_CORTEX_A9:
		/* Get SCU physical base */
		asm("mrc p15, 4, %0, c15, c0, 0" : "=r" (pa));
		scu_base = IO_ADDRESS(pa);
		ncores = scu_get_core_count(scu_base);
		break;
	case ARM_CPU_PART_CORTEX_A15:
	default:
		pr_warn("Unsupported MPIDR %x\n", mpidr);
		ncores = 1;
		break;
	}
	return ncores;
}