linux-kernel - Re: [PATCH] serial: samsung: Continue to work if DMA request fails

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Message-ID: <eaab5961-4b60-cc74-d5bc-5608face822d@math.uni-bielefeld.de>
Date:   Sat, 25 Feb 2017 17:28:41 +0100
From:   Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>
To:     Krzysztof Kozlowski <krzk@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     linux-samsung-soc@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] serial: samsung: Continue to work if DMA request fails

Hello Krzysztof,

Krzysztof Kozlowski wrote:
> If DMA is not available (even when configured in DeviceTree), the driver
> will fail the startup procedure thus making serial console not
> available.
> 
> For example this causes boot failure on QEMU ARMv7 (Exynos4210, SMDKC210):
>     [    1.302575] OF: amba_device_add() failed (-19) for /amba/pdma@...80000
>     ...
>     [   11.435732] samsung-uart 13800000.serial: DMA request failed
>     [   72.963893] samsung-uart 13800000.serial: DMA request failed
>     [   73.143361] Kernel panic - not syncing: Attempted to kill init! exitcode=00000000
> 
> DMA is not necessary for serial to work, so continue with UART startup
> after emitting a warning.
> 
> Fixes: Fixes: 62c37eedb74c ("serial: samsung: add dma reqest/release functions")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
> ---
>  drivers/tty/serial/samsung.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/samsung.c b/drivers/tty/serial/samsung.c
> index b4f86c219db1..7a17aedbf902 100644
> --- a/drivers/tty/serial/samsung.c
> +++ b/drivers/tty/serial/samsung.c
> @@ -1031,8 +1031,10 @@ static int s3c64xx_serial_startup(struct uart_port *port)
>  	if (ourport->dma) {
>  		ret =3c24xx_serial_request_dma(ourport);
>  		if (ret < 0) {
> -			dev_warn(port->dev, "DMA request failed\n");
> -			return ret;
> +			dev_warn(port->dev,
> +				 "DMA request failed, DMA will not be used\n");
> +			devm_kfree(port->dev, ourport->dma);
> +			ourport->dma =ULL;
This line looks odd. Did you want to assign NULL here?
Also, whitespace on both sides of '='?

- Tobias

>  		}
>  	}
>  
>