diff options
Diffstat (limited to 'arch/arm/mach-mvebu/coherency.c')
| -rw-r--r-- | arch/arm/mach-mvebu/coherency.c | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/arch/arm/mach-mvebu/coherency.c b/arch/arm/mach-mvebu/coherency.c index 4e9d58148ca7..c295c10f9217 100644 --- a/arch/arm/mach-mvebu/coherency.c +++ b/arch/arm/mach-mvebu/coherency.c @@ -125,6 +125,29 @@ int __init coherency_init(void) { struct device_node *np; + /* + * The coherency fabric is needed: + * - For coherency between processors on Armada XP, so only + * when SMP is enabled. + * - For coherency between the processor and I/O devices, but + * this coherency requires many pre-requisites (write + * allocate cache policy, shareable pages, SMP bit set) that + * are only meant in SMP situations. + * + * Note that this means that on Armada 370, there is currently + * no way to use hardware I/O coherency, because even when + * CONFIG_SMP is enabled, is_smp() returns false due to the + * Armada 370 being a single-core processor. To lift this + * limitation, we would have to find a way to make the cache + * policy set to write-allocate (on all Armada SoCs), and to + * set the shareable attribute in page tables (on all Armada + * SoCs except the Armada 370). Unfortunately, such decisions + * are taken very early in the kernel boot process, at a point + * where we don't know yet on which SoC we are running. + */ + if (!is_smp()) + return 0; + np = of_find_matching_node(NULL, of_coherency_table); if (np) { struct resource res; @@ -151,6 +174,9 @@ static int __init coherency_late_init(void) { struct device_node *np; + if (!is_smp()) + return 0; + np = of_find_matching_node(NULL, of_coherency_table); if (np) { bus_register_notifier(&platform_bus_type, |