On Friday 14 February 2014 15:54:38 Jisheng Zhang wrote: > Hi all, > > The writel/readl is too expensive especially on Cortex A9 w/ outer L2 cache. This > introduce i2c read/write error on Marvell Berlin SoCs when there are L2 cache > maintenance operations at the same time. > > In our internal berlin bsp, we just replaced readl/writel with the relaxed > version. But AFAIK, the "relaxed" version doesn't exist on all architectures. How > to handle this issue? In case of i2c-designware, this is safe because that driver does not perform DMA. In other drivers, you may have to be more careful, to ensure that all MMIO is serialized with DMA operations performed by the driver. > Any suggestions are appreciated. I would definitely welcome a patch that adds a default _relaxed implementation to include/linux/io.h, like this: #ifndef readb_relaxed #define readb_relaxed(p) readb(p) #endif and then adds "#define readb_relaxed(p) readb_relaxed(p)" etc. to all architectures that have a non-macro definition for readb. Alternatively, we could have a CONFIG_ARCH_MMIO_RELAXED configuration symbol that gets selected by any architecture that provides the _relaxed accessors, and get linux/io.h to define all of them for the other architectures. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
