Subject: [PATCH v3 03/15] ARM: mcpm: introduce helpers for platform coherency exit/setup

From: [email-masked] (Santosh Shilimkar)
Date: Thu, 31 Jan 2013 21:38:23 +0530

On Tuesday 29 January 2013 01:20 PM, Nicolas Pitre wrote:
> From: Dave Martin <[email-masked]>
>
> This provides helper methods to coordinate between CPUs coming down
> and CPUs going up, as well as documentation on the used algorithms,
> so that cluster teardown and setup
> operations are not done for a cluster simultaneously.
>
> For use in the power_down() implementation:
>    * __mcpm_cpu_going_down(unsigned int cluster, unsigned int cpu)
>    * __mcpm_outbound_enter_critical(unsigned int cluster)
>    * __mcpm_outbound_leave_critical(unsigned int cluster)
>    * __mcpm_cpu_down(unsigned int cluster, unsigned int cpu)
>
> The power_up_setup() helper should do platform-specific setup in
> preparation for turning the CPU on, such as invalidating local caches
> or entering coherency.  It must be assembler for now, since it must
> run before the MMU can be switched on.  It is passed the affinity level
> which should be initialized.
>
> Because the mcpm_sync_struct content is looked-up and modified
> with the cache enabled or disabled depending on the code path, it is
> crucial to always ensure proper cache maintenance to update main memory
> right away.  Therefore, any cached write must be followed by a cache
> clean operation and any cached read must be preceded by a cache
> invalidate operation (actually a cache flush i.e. clean+invalidate to
> avoid discarding possible concurrent writes) on the accessed memory.
>
> Also, in order to prevent a cached writer from interfering with an
> adjacent non-cached writer, we ensure each state variable is located to
> a separate cache line.
>
> Thanks to Nicolas Pitre and Achin Gupta for the help with this
> patch.
>
> Signed-off-by: Dave Martin <[email-masked]>
> ---
[..]

> diff --git a/arch/arm/common/mcpm_entry.c b/arch/arm/common/mcpm_entry.c
> index c8c0e2113e..2b83121966 100644
> --- a/arch/arm/common/mcpm_entry.c
> +++ b/arch/arm/common/mcpm_entry.c
> @@ -18,6 +18,7 @@
>   #include <asm/proc-fns.h>
>   #include <asm/cacheflush.h>
>   #include <asm/idmap.h>
> +#include <asm/cputype.h>
>
>   extern volatile unsigned long mcpm_entry_vectors[MAX_NR_CLUSTERS][MAX_CPUS_PER_CLUSTER];
>
[...]

> +/*
> + * Ensure preceding writes to *p by other CPUs are visible to
> + * subsequent reads by this CPU.  We must be careful not to
> + * discard data simultaneously written by another CPU, hence the
> + * usage of flush rather than invalidate operations.
> + */
> +static void __sync_range_r(volatile void *p, size_t size)
> +{
> +	char *_p = (char *)p;
> +
> +#ifdef CONFIG_OUTER_CACHE
> +	if (outer_cache.flush_range) {
> +
You don't need above #ifdef. In case of non-outer
cache the function pointer is null anyways.
		/*
> +		 * Ensure dirty data migrated from other CPUs into our cache
> +		 * are cleaned out safely before the outer cache is cleaned:
> +		 */
> +		__cpuc_clean_dcache_area(_p, size);
> +
> +		/* Clean and invalidate stale data for *p from outer ... */
> +		outer_flush_range(__pa(_p), __pa(_p + size));
> +	}
> +#endif
> +
> +	/* ... and inner cache: */
> +	__cpuc_flush_dcache_area(_p, size);
This will be un-necessary when inner cache is available, no ?
May be you can re-arrange the code like below, unless and until
you would like to invalidate any speculative fetches during the
outer_flush_range()

	__cpuc_clean_dcache_area(_p, size);
	if (outer_cache.flush_range)
		outer_flush_range(__pa(_p), __pa(_p + size));

Rest of the patch looks fine to me.

Regards,
Santosh