linux-kernel - Re: [PATCH v2] serial: imx: fix tx statemachine deadlock

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

Hi Paul,

On Fri, Nov 24, 2023 at 9:55 AM Paul Geurts <paul_geurts@...e.nl> wrote:
>
> 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@...e.nl>