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Relax TX draining in ns8250_bus_transmit().

Description

Relax TX draining in ns8250_bus_transmit().

Since TX interrupt is generated when THRE is set, wait for TEMT set means
wait for full character transmission time. At low speeds that may take
awhile, burning CPU time while holding sc_hwmtx lock, also congested.

This is partial revert of r317659.

PR: 240121
MFC after: 2 weeks

Details

Committed
mavSep 15 2019, 11:56 PM
Parents
rS352368: MFC r349070
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