On 2016-12-02 02:28, Nikita Yushchenko wrote:
> Problem found via lockdep:
>
> - lpuart_set_termios() calls del_timer_sync(&sport->lpuart_timer) while
> holding sport->port.lock
>
> - sport->lpuart_timer routine is lpuart_timer_func() that calls
> lpuart_copy_rx_to_tty() that acquires same lock.
>
> To fix, move Rx DMA stopping out of lock, as it already is in other places
> in the same file.
>
> While at it, also make Rx DMA start/stop code to look the same is in
> other places in the same file.
Yeah I saw that too, never really came around to look closer into it.
Thanks for looking into it.
You removed the check whether there was an old configuration, I think
the idea of that was that we only resize DMA if it was configured
differently before... Not sure how startup/set_termios calls are
ordered. I guess in practice that shouldn't really make a difference
since lpuart_dma_rx_use can't be true until after startup?
One nit below.
--
Stefan
>
> Signed-off-by: Nikita Yushchenko <nikita.yo...@cogentembedded.com>
> ---
> drivers/tty/serial/fsl_lpuart.c | 25 ++++++++++++++-----------
> 1 file changed, 14 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
> index a1c6519837a4..81100c40f33b 100644
> --- a/drivers/tty/serial/fsl_lpuart.c
> +++ b/drivers/tty/serial/fsl_lpuart.c
> @@ -1407,6 +1407,18 @@ lpuart_set_termios(struct uart_port *port,
> struct ktermios *termios,
> /* ask the core to calculate the divisor */
> baud = uart_get_baud_rate(port, termios, old, 50, port->uartclk / 16);
>
> + /*
> + * Need to update the Ring buffer length according to the selected
> + * baud rate and restart Rx DMA path.
> + *
> + * Since timer function acqures sport->port.lock, need to stop before
> + * acquring same lock because otherwise del_timer_sync() can deadlock.
> + */
> + if (sport->lpuart_dma_rx_use) {
> + del_timer_sync(&sport->lpuart_timer);
> + lpuart_dma_rx_free(&sport->port);
> + }
> +
> spin_lock_irqsave(&sport->port.lock, flags);
>
> sport->port.read_status_mask = 0;
> @@ -1456,17 +1468,8 @@ lpuart_set_termios(struct uart_port *port,
> struct ktermios *termios,
> /* restore control register */
> writeb(old_cr2, sport->port.membase + UARTCR2);
>
> - /*
> - * If new baud rate is set, we will also need to update the Ring buffer
> - * length according to the selected baud rate and restart Rx DMA path.
> - */
> - if (old) {
> - if (sport->lpuart_dma_rx_use) {
> - del_timer_sync(&sport->lpuart_timer);
> - lpuart_dma_rx_free(&sport->port);
> - }
> -
> - if (sport->dma_rx_chan && !lpuart_start_rx_dma(sport)) {
> + if (sport->lpuart_dma_rx_use) {
> + if (!lpuart_start_rx_dma(sport)) {
> sport->lpuart_dma_rx_use = true;
No need to set to true here, it is guaranteed to be true at this point.
> rx_dma_timer_init(sport);
> } else {
