do not use sg if not properly supported by usb controller

From: Lorenzo Bianconi <[email protected]>

Use linear fragment and not a single usb scatter-gather buffer in mt76u {tx,rx} datapath if the usb controller has sg data length constraints. Moreover add disable_usb_sg module parameter in order to explicitly disable scatter-gather. SG I/O is not supported by all host drivers and some users have reported sg issues on AMD IOMMU.
This series has been tested on AMD IOMMU cpus/motherboards and on rpi3+

Changes since RFC:
- rebased on top of 'fix multiple issues in mt76u error path'
https://patchwork.kernel.org/cover/10804919/

I am resending the series since the first attempt seems to be rejected by the ML

Lorenzo Bianconi (4):
mt76: usb: move mt76u_check_sg in usb.c
mt76: usb: do not use sg buffers for mcu messages
mt76: usb: use a linear buffer for tx/rx datapath if sg is not
supported
mt76: usb: introduce disable_usb_sg parameter

 drivers/net/wireless/mediatek/mt76/mt76.h     |  14 +-
 .../net/wireless/mediatek/mt76/mt76x0/usb.c   |   2 +-
 .../wireless/mediatek/mt76/mt76x02_usb_mcu.c  |   3 +-
 .../wireless/mediatek/mt76/mt76x2/usb_init.c  |   2 +-
 drivers/net/wireless/mediatek/mt76/usb.c      | 133 +++++++++++++-----
 drivers/net/wireless/mediatek/mt76/usb_mcu.c  |   5 +-
 6 files changed, 105 insertions(+), 54 deletions(-)

2.20.1