Am Dienstag, 16. Februar 2010 14:40:45 schrieb Shilimkar, Santosh: > > > If the CPU writes to a DMA_FROM_DEVICE buffer between map and unmap, the > > > writes can sit in the cache, and on unmap, they will be discarded. > > > > > > Cleaning the cache on unmap is not an option; that too can lead to DMA > > > buffer corruption in the DMA case. > > > > I am afraid for these controllers the controller driver must be responsible > > for all DMA and cache issues. Indicating the exact requirements to the > > upper layer would be a battle already lost. > > so the safe choice is not to set has_dma and the generic layer will leave > > the issue to the lower level. > This means don't use dma at all which will almost kill the performance. Why would you be unable to map a buffer in the hcd driver when you know that you'll use DMA? Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
