On Saturday 14 April 2012 06:54 PM, Russell King - ARM Linux wrote: > Using coherent DMA memory with the OMAP DMA engine results in > unpredictable behaviour due to memory ordering issues; as things stand, > there is no guarantee that data written to coherent DMA memory will be > visible to the DMA hardware. > > This is because the OMAP dma_write() accessor contains no barriers, > necessary on ARMv6 and above. The effect of this can be seen in comments > in the OMAP serial driver, which incorrectly talks about cache flushing > for the coherent DMA stuff. > > Rather than adding barriers to the accessors, add it in the DMA support > code just before we enable DMA, and just after we disable DMA. This > avoids having barriers for every DMA register access. > > Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx> > --- I don't why the synchronisation in dma_[start/stop] was missing. The patch indeed make complete sense. > Is this why no one uses DMA with the serial driver? > Will check if this patch helps in some of the DMA issues seen in serial driver. Regards Santosh -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
