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From:   Fabio Estevam <festevam@gmail.com>
Date:   Fri, 24 Nov 2023 09:58:19 -0300
Message-ID: <CAOMZO5AgDjwUeePO4ibUeKkpf-YV9v=Dws0S01HMERdDf85yoQ@mail.gmail.com>
Subject: Re: [PATCH v2] serial: imx: fix tx statemachine deadlock
To:     Paul Geurts <paul_geurts@live.nl>
Cc:     gregkh@linuxfoundation.org, jirislaby@kernel.org,
        shawnguo@kernel.org, s.hauer@pengutronix.de, kernel@pengutronix.de,
        linux-imx@nxp.com, u.kleine-koenig@pengutronix.de,
        linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org
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Hi Paul,

On Fri, Nov 24, 2023 at 9:55=E2=80=AFAM Paul Geurts <paul_geurts@live.nl> w=
rote:
>
> When using the serial port as RS485 port, the tx statemachine is used to
> control the RTS pin to drive the RS485 transceiver TX_EN pin. When the
> TTY port is closed in the middle of a transmission (for instance during
> userland application crash), imx_uart_shutdown disables the interface
> and disables the Transmission Complete interrupt. afer that,
> imx_uart_stop_tx bails on an incomplete transmission, to be retriggered
> by the TC interrupt. This interrupt is disabled and therefore the tx
> statemachine never transitions out of SEND. The statemachine is in
> deadlock now, and the TX_EN remains low, making the interface useless.
>
> imx_uart_stop_tx now checks for incomplete transmission AND whether TC
> interrupts are enabled before bailing to be retriggered. This makes sure
> the state machine handling is reached, and is properly set to
> WAIT_AFTER_SEND.
>
> Fixes: cb1a60923609 serial: imx: implement rts delaying for rs485

One nit: the correct format for the Fixes tag is:

Fixes: cb1a60923609 ("serial: imx: implement rts delaying for rs485")

And no blank line is needed between the Fixes and Signed-off-by line.

> Signed-off-by: Paul Geurts <paul_geurts@live.nl>