Following the discussion on PWC [1] and UVC [2] drivers, where
use non-consistent mappings for the URB transfer buffers was
shown to improve transfer speed significantly, here's a proposal
for a non-coherent USB helpers.
With this pachset, it's possible to get 360x288 raw analog video
using stk1160 and a AM335x Beaglebone Black board. This isn't
possible in mainline, for the same reasons Matwey has explained [1].
First patch is a hack, obviously incomplete, to add support for
non-consistent mappings on ARM.
The second patch introduces the usb_{alloc,free}_noncoherent API,
while the third patch is an example on stk1160.
I'm sending this patchset as RFC, just to get the ball rolling.
[1] https://lkml.org/lkml/2018/8/21/663
[2] https://lkml.org/lkml/2018/6/27/188
Ezequiel Garcia (3):
HACK: ARM: dma-mapping: Get writeback memory for non-consistent
mappings
USB: core: Add non-coherent buffer allocation helpers
stk1160: Use non-coherent buffers for USB transfers
arch/arm/include/asm/pgtable.h | 3 ++
arch/arm/mm/dma-mapping.c | 9 ++--
drivers/media/usb/stk1160/stk1160-video.c | 22 +++------
drivers/usb/core/buffer.c | 29 +++++++-----
drivers/usb/core/hcd.c | 5 +-
drivers/usb/core/usb.c | 56 ++++++++++++++++++++++-
include/linux/usb.h | 5 ++
include/linux/usb/hcd.h | 4 +-
8 files changed, 97 insertions(+), 36 deletions(-)
--
2.18.0
