RE: [EXT] [PATCH v2 1/2] tty: serial: fsl_lpuart: move dma_request_chan()

[Andy Duan <fugang.duan@nxp.com>]

From: Michael Walle <michael@walle.cc> Sent: Wednesday, March 25, 2020 5:07 PM
> Move dma_request_chan() out of the atomic context. First this call should not
> be in the atomic context at all and second the
> dev_info_once() may cause a hang because because the console takes this
> spinlock, too.
> 
> Fixes: 159381df1442f ("tty: serial: fsl_lpuart: fix DMA operation when using
> IOMMU")
> Reported-by: Leonard Crestez <leonard.crestez@nxp.com>
> Signed-off-by: Michael Walle <michael@walle.cc>

Reviewed-by: Fugang Duan <fugang.duan@nxp.com>

> ---
> changes since v1:
>  - instead of just moving the dev_info_once() out of the spinlock protected
>    section, move the whole dma_request_chan(). Thanks Andy!
> 
> I've tested this on my board. Andy, Leonard, can you double check it? For all
> which are not aware, this deadlock happens only if you have the kernel
> console output on the lpuart, so if someone wants to test it, make sure you
> have something like console=ttyLP0,115200.
> 
>  drivers/tty/serial/fsl_lpuart.c | 36 +++++++++++++++++++++------------
>  1 file changed, 23 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c index
> 9c6a018b1390..131018979b77 100644
> --- a/drivers/tty/serial/fsl_lpuart.c
> +++ b/drivers/tty/serial/fsl_lpuart.c
> @@ -1510,20 +1510,33 @@ static void rx_dma_timer_init(struct lpuart_port
> *sport)
>         add_timer(&sport->lpuart_timer);  }
> 
> -static void lpuart_tx_dma_startup(struct lpuart_port *sport)
> +static void lpuart_request_dma(struct lpuart_port *sport)
>  {
> -       u32 uartbaud;
> -       int ret;
> -
>         sport->dma_tx_chan = dma_request_chan(sport->port.dev, "tx");
>         if (IS_ERR(sport->dma_tx_chan)) {
>                 dev_info_once(sport->port.dev,
>                               "DMA tx channel request failed,
> operating without tx DMA (%ld)\n",
>                               PTR_ERR(sport->dma_tx_chan));
>                 sport->dma_tx_chan = NULL;
> -               goto err;
>         }
> 
> +       sport->dma_rx_chan = dma_request_chan(sport->port.dev, "rx");
> +       if (IS_ERR(sport->dma_rx_chan)) {
> +               dev_info_once(sport->port.dev,
> +                             "DMA rx channel request failed,
> operating without rx DMA (%ld)\n",
> +                             PTR_ERR(sport->dma_rx_chan));
> +               sport->dma_rx_chan = NULL;
> +       }
> +}
> +
> +static void lpuart_tx_dma_startup(struct lpuart_port *sport) {
> +       u32 uartbaud;
> +       int ret;
> +
> +       if (!sport->dma_tx_chan)
> +               goto err;
> +
>         ret = lpuart_dma_tx_request(&sport->port);
>         if (!ret)
>                 goto err;
> @@ -1549,14 +1562,8 @@ static void lpuart_rx_dma_startup(struct
> lpuart_port *sport)  {
>         int ret;
> 
> -       sport->dma_rx_chan = dma_request_chan(sport->port.dev, "rx");
> -       if (IS_ERR(sport->dma_rx_chan)) {
> -               dev_info_once(sport->port.dev,
> -                             "DMA rx channel request failed,
> operating without rx DMA (%ld)\n",
> -                             PTR_ERR(sport->dma_rx_chan));
> -               sport->dma_rx_chan = NULL;
> +       if (!sport->dma_rx_chan)
>                 goto err;
> -       }
> 
>         ret = lpuart_start_rx_dma(sport);
>         if (ret)
> @@ -1592,6 +1599,8 @@ static int lpuart_startup(struct uart_port *port)
>         sport->rxfifo_size = UARTFIFO_DEPTH((temp >>
> UARTPFIFO_RXSIZE_OFF) &
> 
> UARTPFIFO_FIFOSIZE_MASK);
> 
> +       lpuart_request_dma(sport);
> +
>         spin_lock_irqsave(&sport->port.lock, flags);
> 
>         lpuart_setup_watermark_enable(sport);
> @@ -1649,11 +1658,12 @@ static int lpuart32_startup(struct uart_port
> *port)
>                 sport->port.fifosize = sport->txfifo_size;
>         }
> 
> +       lpuart_request_dma(sport);
> +
>         spin_lock_irqsave(&sport->port.lock, flags);
> 
>         lpuart32_setup_watermark_enable(sport);
> 
> -
>         lpuart_rx_dma_startup(sport);
>         lpuart_tx_dma_startup(sport);
> 
> --
> 2.20.1