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

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Date:   Wed, 4 Oct 2023 14:13:01 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Paul Geurts <paul_geurts@...e.nl>
Cc:     jirislaby@...nel.org, shawnguo@...nel.org, s.hauer@...gutronix.de,
        kernel@...gutronix.de, festevam@...il.com, linux-imx@....com,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] serial: imx: fix tx statemachine deadlock

On Wed, Oct 04, 2023 at 11:57:22AM +0200, Paul Geurts 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.
> 
> Signed-off-by: Paul Geurts <paul_geurts@...e.nl>
> ---
>  drivers/tty/serial/imx.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

What commit id does this fix?

thanks,

greg k-h