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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>
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