linux-kernel - Re: [PATCH v2 1/2] tty: serial: fsl_lpuart: move dma_request

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Date:   Wed, 25 Mar 2020 18:05:16 +0000
From:   Leonard Crestez <leonard.crestez@....com>
To:     Michael Walle <michael@...le.cc>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jiri Slaby <jslaby@...e.com>, Andy Duan <fugang.duan@....com>
Subject: Re: [PATCH v2 1/2] tty: serial: fsl_lpuart: move dma_request_chan()

On 2020-03-25 11:07 AM, Michael Walle wrote:
> 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@....com>
> Signed-off-by: Michael Walle <michael@...le.cc>
> ---
> 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(-)

Tested-by: Leonard Crestez <leonard.crestez@....com>

Since the original commit only made it into next it might make sense to 
squash the commits in the tty tree.

This way future bisections won't get stuck on a boot failure.

> 
> 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);
>   
>