Re: [PATCH 2/2] tty: serial: lpuart: disable hardware flow control in lpuart32_startup()

[sashiko-bot@kernel.org]

> From: Sherry Sun <sherry.sun@nxp.com>
> 
> The RXRTSE/TXCTSE bits in UARTMODIR are configured by set_termios()
> according to CRTSCTS and are left untouched by shutdown(), so they keep
> their value from the previous session when the port is started again.
> 
> On open, and on resume when a tty is attached, the serial core calls
> ops->startup() before set_termios(). lpuart32_startup() enables the
> receiver (UARTCTRL_RE), and with RXRTSE still set from the previous
> session RTS is asserted immediately. The remote side may then start
> sending before set_termios() deasserts RTS again, disables TE/RE and
> reprograms the baud rate, so the characters in flight are lost or
> corrupted.
> 
> Clear RXRTSE/TXCTSE at the beginning of lpuart32_startup() instead.
> Together with set_termios() keeping both bits masked until its last
> UARTMODIR write, RTS now stays deasserted from startup() until the port
> is fully configured. The flow control setting itself is still owned by
> set_termios().
> 
> Fixes: 380c966c093e ("tty: serial: fsl_lpuart: add 32-bit register interface support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sherry Sun <sherry.sun@nxp.com>

Sashiko has reviewed this patch and found no issues.

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