Re: [PATCH] ARM: kernel: DT cpu map validity check helper function

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Thu, Jan 10, 2013 at 12:15:14PM +0000, Dave Martin wrote:
> On Thu, Jan 10, 2013 at 11:48:27AM +0000, Lorenzo Pieralisi wrote:
> > Since the introduction of /cpu nodes bindings for ARM and the
> > corresponding parse function arm_dt_init_cpu_maps(), the cpu_logical_map
> > and the number of possible CPUs are set according to the DT /cpu
> > nodes entries. Currently most of the existing ARM SMP platforms detect the
> > number of cores through HW probing in their .smp_init_cpus functions and set
> > the possible CPU mask accordingly.
> > This method should be upgraded so that the CPU counting mechanism will be
> > based on DT, keeping legacy HW probing mechanism as a fall back solution.
> > 
> > In order to implement this fall back solution mechanism, the ARM DT code
> > should provide a helper function to platforms to check if the cpu map
> > has been properly initialized through DT. If the check fails the
> > platform will resort to legacy HW based cores counting mechanism.
> > 
> > This patch implements a trivial flag and a helper function that platform
> > can call to check whether DT based cpu map initialization and cores count
> > were completed successfully.
> > 
> > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> > ---
> >  arch/arm/include/asm/prom.h | 10 ++++++++++
> >  arch/arm/kernel/devtree.c   |  5 +++++
> >  2 files changed, 15 insertions(+)
> > 
> > diff --git a/arch/arm/include/asm/prom.h b/arch/arm/include/asm/prom.h
> > index a219227..487614a 100644
> > --- a/arch/arm/include/asm/prom.h
> > +++ b/arch/arm/include/asm/prom.h
> > @@ -18,6 +18,15 @@
> >  extern struct machine_desc *setup_machine_fdt(unsigned int dt_phys);
> >  extern void arm_dt_memblock_reserve(void);
> >  extern void __init arm_dt_init_cpu_maps(void);
> > +/*
> > + * Return true if cpu map initialization has been
> > + * carried out correctly from DT
> > + */
> > +static inline bool __init arm_dt_cpu_map_valid(void)
> > +{
> > +	extern bool valid_dt_cpu_map;
> > +	return valid_dt_cpu_map;
> > +}
> >  
> >  #else /* CONFIG_OF */
> >  
> > @@ -28,6 +37,7 @@ static inline struct machine_desc *setup_machine_fdt(unsigned int dt_phys)
> >  
> >  static inline void arm_dt_memblock_reserve(void) { }
> >  static inline void arm_dt_init_cpu_maps(void) { }
> > +static inline bool __init arm_dt_cpu_map_valid(void) { return false; }
> >  
> >  #endif /* CONFIG_OF */
> >  #endif /* ASMARM_PROM_H */
> > diff --git a/arch/arm/kernel/devtree.c b/arch/arm/kernel/devtree.c
> > index 70f1bde..c82af3b 100644
> > --- a/arch/arm/kernel/devtree.c
> > +++ b/arch/arm/kernel/devtree.c
> > @@ -62,6 +62,10 @@ void __init arm_dt_memblock_reserve(void)
> >  		memblock_reserve(base, size);
> >  	}
> >  }
> > +/*
> > + * Export DT cpu map validity flag to platforms
> > + */
> > +bool valid_dt_cpu_map __initdata;
> 
> Is there any possibility of this being useful after boot?
> Hopefully not, but maybe there's something I haven't considered.

I do not think so, at least for the use cases I have envisaged at the moment,
but it is certainly something I should consider.

Thanks,
Lorenzo