On 25/04/2017 20:15, Geert Uytterhoeven wrote:
> If DMA is enabled and used, a burst of old data may be seen on the
> serial console during "poweroff" or "reboot". uart_flush_buffer()
> clears the circular buffer, but sci_port.tx_dma_len is not reset.
> This leads to a circular buffer overflow, dumping (UART_XMIT_SIZE -
> sci_port.tx_dma_len) bytes.
>
> To fix this, add a .flush_buffer() callback that resets
> sci_port.tx_dma_len.
>
> Inspired by commit 31ca2c63fdc0aee7 ("tty/serial: atmel: fix race
> condition (TX+DMA)").
>
> Signed-off-by: Geert Uytterhoeven <geert+rene...@glider.be>
> ---
> A big thanks to Richard!
> I had no idea what was happening here, until I saw his patch passing by
> in a stable backport.
:)
you're welcome !
> In v4.3 and older, the field is called sg_len_tx.
> ---
> drivers/tty/serial/sh-sci.c | 16 ++++++++++++++--
> 1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
> index 9a47cc4f16a2798f..a15739202d6c75f2 100644
> --- a/drivers/tty/serial/sh-sci.c
> +++ b/drivers/tty/serial/sh-sci.c
> @@ -1545,7 +1545,16 @@ static void sci_free_dma(struct uart_port *port)
> if (s->chan_rx)
> sci_rx_dma_release(s, false);
> }
> -#else
> +
> +static void sci_flush_buffer(struct uart_port *port)
> +{
> + /*
> + * In uart_flush_buffer(), the xmit circular buffer has just been
> + * cleared, so we have to reset tx_dma_len accordingly.
> + */
> + to_sci_port(port)->tx_dma_len = 0;
> +}
> +#else /* !CONFIG_SERIAL_SH_SCI_DMA */
> static inline void sci_request_dma(struct uart_port *port)
> {
> }
> @@ -1553,7 +1562,9 @@ static inline void sci_request_dma(struct uart_port
> *port)
> static inline void sci_free_dma(struct uart_port *port)
> {
> }
> -#endif
> +
> +#define sci_flush_buffer NULL
> +#endif /* !CONFIG_SERIAL_SH_SCI_DMA */
>
> static irqreturn_t sci_rx_interrupt(int irq, void *ptr)
> {
> @@ -2566,6 +2577,7 @@ static const struct uart_ops sci_uart_ops = {
> .break_ctl = sci_break_ctl,
> .startup = sci_startup,
> .shutdown = sci_shutdown,
> + .flush_buffer = sci_flush_buffer,
> .set_termios = sci_set_termios,
> .pm = sci_pm,
> .type = sci_type,
>
