On Thursday 15 May 2014 11:18:38 Thomas Petazzoni wrote: > When a PL310 cache is used on a system that provides hardware > coherency, the outer cache sync operation is useless, and can be > skipped. Moreover, on some systems, it is harmful as it causes > deadlocks between the Marvell coherency mechanism, the Marvell PCIe > controller and the Cortex-A9. > > To avoid this, this commit introduces a new Device Tree property > 'dma-coherent' for the L2 cache controller node, valid only for the > PL310 cache. It identifies the usage of the PL310 cache in an I/O > coherent configuration. Internally, it makes the driver use a > different set of l2x0_of_data, in which the ->sync operation is NULL. > > Note that technically speaking, a fully coherent system wouldn't > require any of the other .outer_cache operations. However, in > practice, when booting secondary CPUs, these are not yet coherent, and > therefore a set of cache maintenance operations are necessary at this > point. This explains why we keep the other .outer_cache operations and > only ->sync is disabled. > > While in theory any write to a PL310 register could cause the > deadlock, in practice, disabling ->sync is sufficient to workaround > the deadlock, since the other cache maintenance operations are only > used in very specific situations. > > Signed-off-by: Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxxxxxxxxx> > Acked-by: Arnd Bergmann <arnd@xxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
