USB: usb/dma doc updates
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>
2 files changed