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From:   Leonard Crestez <leonard.crestez@nxp.com>
To:     Michael Walle <michael@walle.cc>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC:     "linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Jiri Slaby <jslaby@suse.com>, Andy Duan <fugang.duan@nxp.com>
Subject: Re: [PATCH v2 1/2] tty: serial: fsl_lpuart: move dma_request_chan()
Thread-Topic: [PATCH v2 1/2] tty: serial: fsl_lpuart: move dma_request_chan()
Thread-Index: AQHWAoTFxHV8sVlM60KMfOo/y+nDDA==
Date:   Wed, 25 Mar 2020 18:05:16 +0000
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On 2020-03-25 11:07 AM, Michael Walle wrote:=0A=
> Move dma_request_chan() out of the atomic context. First this call=0A=
> should not be in the atomic context at all and second the=0A=
> dev_info_once() may cause a hang because because the console takes this=
=0A=
> spinlock, too.=0A=
> =0A=
> Fixes: 159381df1442f ("tty: serial: fsl_lpuart: fix DMA operation when us=
ing IOMMU")=0A=
> Reported-by: Leonard Crestez <leonard.crestez@nxp.com>=0A=
> Signed-off-by: Michael Walle <michael@walle.cc>=0A=
> ---=0A=
> changes since v1:=0A=
>   - instead of just moving the dev_info_once() out of the spinlock protec=
ted=0A=
>     section, move the whole dma_request_chan(). Thanks Andy!=0A=
> =0A=
> I've tested this on my board. Andy, Leonard, can you double check it? For=
=0A=
> all which are not aware, this deadlock happens only if you have the kerne=
l=0A=
> console output on the lpuart, so if someone wants to test it, make sure y=
ou=0A=
> have something like console=3DttyLP0,115200.=0A=
> =0A=
>   drivers/tty/serial/fsl_lpuart.c | 36 +++++++++++++++++++++------------=
=0A=
>   1 file changed, 23 insertions(+), 13 deletions(-)=0A=
=0A=
Tested-by: Leonard Crestez <leonard.crestez@nxp.com>=0A=
=0A=
Since the original commit only made it into next it might make sense to =0A=
squash the commits in the tty tree.=0A=
=0A=
This way future bisections won't get stuck on a boot failure.=0A=
=0A=
> =0A=
> diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpu=
art.c=0A=
> index 9c6a018b1390..131018979b77 100644=0A=
> --- a/drivers/tty/serial/fsl_lpuart.c=0A=
> +++ b/drivers/tty/serial/fsl_lpuart.c=0A=
> @@ -1510,20 +1510,33 @@ static void rx_dma_timer_init(struct lpuart_port =
*sport)=0A=
>   	add_timer(&sport->lpuart_timer);=0A=
>   }=0A=
>   =0A=
> -static void lpuart_tx_dma_startup(struct lpuart_port *sport)=0A=
> +static void lpuart_request_dma(struct lpuart_port *sport)=0A=
>   {=0A=
> -	u32 uartbaud;=0A=
> -	int ret;=0A=
> -=0A=
>   	sport->dma_tx_chan =3D dma_request_chan(sport->port.dev, "tx");=0A=
>   	if (IS_ERR(sport->dma_tx_chan)) {=0A=
>   		dev_info_once(sport->port.dev,=0A=
>   			      "DMA tx channel request failed, operating without tx DMA (%ld)=
\n",=0A=
>   			      PTR_ERR(sport->dma_tx_chan));=0A=
>   		sport->dma_tx_chan =3D NULL;=0A=
> -		goto err;=0A=
>   	}=0A=
>   =0A=
> +	sport->dma_rx_chan =3D dma_request_chan(sport->port.dev, "rx");=0A=
> +	if (IS_ERR(sport->dma_rx_chan)) {=0A=
> +		dev_info_once(sport->port.dev,=0A=
> +			      "DMA rx channel request failed, operating without rx DMA (%ld)\=
n",=0A=
> +			      PTR_ERR(sport->dma_rx_chan));=0A=
> +		sport->dma_rx_chan =3D NULL;=0A=
> +	}=0A=
> +}=0A=
> +=0A=
> +static void lpuart_tx_dma_startup(struct lpuart_port *sport)=0A=
> +{=0A=
> +	u32 uartbaud;=0A=
> +	int ret;=0A=
> +=0A=
> +	if (!sport->dma_tx_chan)=0A=
> +		goto err;=0A=
> +=0A=
>   	ret =3D lpuart_dma_tx_request(&sport->port);=0A=
>   	if (!ret)=0A=
>   		goto err;=0A=
> @@ -1549,14 +1562,8 @@ static void lpuart_rx_dma_startup(struct lpuart_po=
rt *sport)=0A=
>   {=0A=
>   	int ret;=0A=
>   =0A=
> -	sport->dma_rx_chan =3D dma_request_chan(sport->port.dev, "rx");=0A=
> -	if (IS_ERR(sport->dma_rx_chan)) {=0A=
> -		dev_info_once(sport->port.dev,=0A=
> -			      "DMA rx channel request failed, operating without rx DMA (%ld)\=
n",=0A=
> -			      PTR_ERR(sport->dma_rx_chan));=0A=
> -		sport->dma_rx_chan =3D NULL;=0A=
> +	if (!sport->dma_rx_chan)=0A=
>   		goto err;=0A=
> -	}=0A=
>   =0A=
>   	ret =3D lpuart_start_rx_dma(sport);=0A=
>   	if (ret)=0A=
> @@ -1592,6 +1599,8 @@ static int lpuart_startup(struct uart_port *port)=
=0A=
>   	sport->rxfifo_size =3D UARTFIFO_DEPTH((temp >> UARTPFIFO_RXSIZE_OFF) &=
=0A=
>   					    UARTPFIFO_FIFOSIZE_MASK);=0A=
>   =0A=
> +	lpuart_request_dma(sport);=0A=
> +=0A=
>   	spin_lock_irqsave(&sport->port.lock, flags);=0A=
>   =0A=
>   	lpuart_setup_watermark_enable(sport);=0A=
> @@ -1649,11 +1658,12 @@ static int lpuart32_startup(struct uart_port *por=
t)=0A=
>   		sport->port.fifosize =3D sport->txfifo_size;=0A=
>   	}=0A=
>   =0A=
> +	lpuart_request_dma(sport);=0A=
> +=0A=
>   	spin_lock_irqsave(&sport->port.lock, flags);=0A=
>   =0A=
>   	lpuart32_setup_watermark_enable(sport);=0A=
>   =0A=
> -=0A=
>   	lpuart_rx_dma_startup(sport);=0A=
>   	lpuart_tx_dma_startup(sport);=0A=
>   =0A=
> =0A=
=0A=