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

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Date:   Sat, 25 Feb 2017 18:34:59 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>
Cc:     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,
        linux-samsung-soc@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] serial: samsung: Continue to work if DMA request fails

On Sat, Feb 25, 2017 at 05:28:41PM +0100, Tobias Jakobi wrote:
> 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 '='?

Ugh, I must ate it by mistake somehow because my git contains proper
"NULL" here.

Thanks for pointing this, I'll resend v3.


Best regards,
Krzysztof