Re: [PATCH v6 3/5] serial: core: allow drivers to reserve flushed transmit storage

[sashiko-bot@kernel.org]

> uart_flush_buffer() resets the transmit FIFO before calling the driver's
> flush callback. An asynchronous DMA transfer can still access that storage
> after the callback returns, while a new write can immediately reuse it.
> 
> Add uart_xmit_block() and uart_xmit_unblock() so a driver can reserve the
> flushed storage until its transfer and completion callbacks have retired.
> Serialize the reservation with FIFO producers using the port lock.
> 
> While the storage is reserved, write_room() reports no space and write()
> and put_char() accept no data. Defer write-ready notifications until the
> reservation is released, preserving one-shot TTY wakeups. Keep the flush
> wakeup under the port lock so it cannot race another reservation.
> 
> Suppress ordinary TX starts while the FIFO storage is blocked. Preserve
> high-priority flow-control characters, which use separate storage.
> [ ... ]
> Publish resume readiness under the same port lock as the TX restart,
> without clearing any reservation. A concurrent flush can then reserve a
> new transfer without resume releasing its storage prematurely.
> 
> Signed-off-by: James Hilliard <james.hilliard1@gmail.com>

Sashiko has reviewed this patch and found no issues.

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