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

[Hiroshi Doyu]

Hi Lorenzo,

Lorenzo Pieralisi <lorenzo.pieralisi at arm.com> wrote @ Tue, 8 Jan 2013 18:11:03 +0100:

> On Tue, Jan 08, 2013 at 04:21:38PM +0000, Mark Rutland wrote:
> > On Tue, Jan 08, 2013 at 02:53:42PM +0000, Hiroshi Doyu wrote:
> 
> [...]
> 
> > > > >  static void __init tegra_smp_init_cpus(void)
> > > > >  {
> > > > > -	unsigned int i, ncores = scu_get_core_count(scu_base);
> > > > > +	unsigned int i, cpu_id, ncores;
> > > > > +	u32 l2ctlr;
> > > > > +	phys_addr_t pa;
> > > > > +
> > > > > +	cpu_id = read_cpuid(CPUID_ID) & CPU_MASK;
> > > > > +	switch (cpu_id) {
> > > > > +	case CPU_CORTEX_A15:
> > > > > +		asm("mrc p15, 1, %0, c9, c0, 2\n" : "=r" (l2ctlr));
> > > > > +		ncores = ((l2ctlr >> 24) & 3) + 1;
> > > > > +		break;
> > > > 
> > > > [...]
> > > > 
> > > > As mentioned last time [1], you should get this information from the dt
> > > > instead.
> > > 
> > > Most of platsmp.c:.smp_init_cpus() implementations seem just to
> > > overwrite # of cores by SCU/MRC detection. Is there any implementation
> > > to use the DT's # and skip SCU/MRC detection in .smp_init_cpus()?
> > 
> > As far as I can see, there's no other platform which just relies on
> > arm_dt_init_cpu_maps. Until recently, it didn't exist, so that makes some
> > sense. As far as I can see, for the Tegra 114 you only need your smp_init_cpus
> > to call set_smp_cross_call(gic_raise_softirq). Everything else you do seems to
> > be handled by arm_dt_init_cpus.
> > 
> > I think the best option would be to have a separate smp_ops for your dt
> > platforms where we know cpu nodes are populated (e.g. Tegra 114), where
> > smp_init_cpus is different to that for non-dt platforms. That way non dt
> > platforms can keep the SCU hack for now, and won't be broken, and the dt
> > platforms are far removed from the SCU hack and just use common infrastructure.
> > 
> > Maybe someone else has a better idea?
> 
> Have a look at mach-vexpress/platsmp.c (keeping in mind that the
> GENERIC_SCU case will be refactored/removed since arm_dt_init_cpu_maps() is
> doing most of the required steps), please let me know what you think.

In tegra, we don't support non-DT. What about falling back SCU/MRC
based detection only when arm_dt_init_cpu_maps() fails?

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();
 
 	set_smp_cross_call(gic_raise_softirq);
 }