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usb: dwc2: masquerade split-interrupt transfers #6936

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@P33M P33M commented Jul 4, 2025

Second attempt at porting the dwc_otg hack to avoid dropped split transactions.

Transactions now "look OK" on the bus analyser but this needs more soak testing with different hub implementations.

P33M added 2 commits July 4, 2025 10:10
Masquerading Interrupt split transfers as Control puts the transfer into
the non-periodic handler in the hub. This stops the hub dropping
complete-split data in the microframe after a CSPLIT should have
arrived, improving resilience to host IRQ latency. Devices are none
the wiser - the handshake tokens are the same.

Originally devised by Hans Petter Selasky @ FreeBSD.

(v2: dwc2 needs an un-masquerade prior to channel interrupt handling)

Signed-off-by: Jonathan Bell <[email protected]>
Control Setup phase transfers needs an 8 byte maxpacket override, or
drivers doing a GET with a small buffer as a split transaction would
cause broken transfers.

Signed-off-by: Jonathan Bell <[email protected]>
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