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usb: gadget: ncm: Add support to update wMaxSegmentSize via configfs

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The max segment size is currently limited to the ethernet frame length of
the kernel which happens to be 1514 at this point in time. However the NCM
specification limits it to 64K for sixtenn bit NTB's. For peer to peer
connections, increasing the segment size gives better throughput.

Add support to configure this value before configfs symlink is created.
Also since the NTB Out/In buffer sizes are fixed at 16384 bytes, limit the
segment size to an upper cap of 8000 to allow at least a minimum of 2 MTU
sized datagrams to be aggregated.

Set the default MTU size for the ncm interface during function bind before
network interface is registered allowing MTU to be set in parity with
wMaxSegmentSize.

Update gadget documentation describing the new configfs property.

Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>
Link: https://lore.kernel.org/r/20231221153216.18657-1-quic_kriskura@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Krishna Kurapati
2023-12-21 21:02:16 +05:30
committed by Greg Kroah-Hartman
parent 68c26fe581
commit 1900daeefd
3 changed files with 79 additions and 12 deletions
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20
Documentation/usb/gadget-testing.rst
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@@ -448,15 +448,17 @@ Function-specific configfs interface
The function name to use when creating the function directory is "ncm".
The NCM function provides these attributes in its function directory:
=============== ==================================================
ifname network device interface name associated with this
function instance
qmult queue length multiplier for high and super speed
host_addr MAC address of host's end of this
Ethernet over USB link
dev_addr MAC address of device's end of this
Ethernet over USB link
=============== ==================================================
=============== ==================================================
ifname network device interface name associated with this
function instance
qmult queue length multiplier for high and super speed
host_addr MAC address of host's end of this
Ethernet over USB link
dev_addr MAC address of device's end of this
Ethernet over USB link
max_segment_size Segment size required for P2P connections. This
will set MTU to (max_segment_size - 14 bytes)
=============== ==================================================
and after creating the functions/ncm.<instance name> they contain default
values: qmult is 5, dev_addr and host_addr are randomly selected.