On Fri, Jul 10, 2009 at 03:11:29PM +0000, James Bottomley wrote: > The design of coherent memory was for memory based device mailboxes > managed by the kernel ... trying to give userspace coherent access to > the same mailbox is problematic because it gives a direct way for the > process to interfere with a device function ... shouldn't whatever > you're trying to do be better accomplished by using an API to control > the device and keeping the coherent mailbox fully in the kernel address > space? As far as sound DMA goes, it's not about mailboxes. It's about a circular buffer which you want the device to DMA from direct to/from the DAC/ADC and have the application write/read data directly to/from that same buffer. Without this, you end up having to copy the sound data - at something around 200KB/s from applications into a driver managed buffer, which is quite an unnecessary overhead for the CPU. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
