fix(dwc2): queue initial slave OUT packet immediately

In slave mode, channel_xfer_start() enabled an OUT channel but left every FIFO write to a later PTXFEMP interrupt. DWC2 creates the request-queue entry only when the packet's final FIFO word is written, so unrelated interrupt work could consume the selected service frame before the transfer was actually queued.

Factor FIFO writes into a capacity-checked helper and write the initial packet while the channel-enable operation is still protected from DWC2 interrupts. Keep FIFO-empty interrupts only for data that does not fit immediately. The protected section never waits for FIFO or request-queue space.

When initial periodic OUT submission is too close to the frame boundary, release the unused channel and defer the still-pending endpoint to the next SOF. Internal retries bypass this initial boundary guard.

A hardware trace showed HCCHAR enabled for frame 0x0378 while the packet's final FIFO word was delayed until frame 0x03ae. The complete five-commit fix set passed 600 seconds in every O0/O2 and slave/DMA mode.

Signed-off-by: HiFiPHile <[email protected]>

0 files changed, 0 insertions, 0 deletions