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fbf54dd320
This patch updates some of the documentation about DMA buffer management for USB, and ways to avoid extra copying. Our understanding of the issues has improved over time. - Most drivers should *avoid* the dma-coherent allocators. There are a few exceptions (like the HID driver). - Some methods are currently commented out; it seems folk writing USB drivers aren't doing performance tuning at that level yet. - Just avoid highmem; there's no good way to pass an "I can do highmem DMA" capability through a driver stack. This is easy, everything already avoids highmem. But it'd be nice if x86_32 systems with much physical memory could use it directly with network adapters and mass storage devices. (Patch, anyone?) Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>