linux-kernel - Re: [PATCH v4 4/4] gnss: add driver for mediatek receivers

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Date:   Thu, 14 Feb 2019 11:12:12 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Corentin Labbe <clabbe.montjoie@...il.com>
Cc:     Loys Ollivier <lollivier@...libre.com>, devicetree@...r.kernel.org,
        Johan Hovold <johan@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Kevin Hilman <khilman@...libre.com>,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        linux-mediatek@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 4/4] gnss: add driver for mediatek receivers

On Thu, Feb 14, 2019 at 11:00:19AM +0100, Corentin Labbe wrote:
> On Wed, Feb 13, 2019 at 04:09:29PM +0100, Loys Ollivier wrote:
> > Add driver for serial-connected Mediatek-based GNSS receivers.
> > 
> > These devices typically boot transmitting vendor specific NMEA output
> > sequences. The serial port bit rate is read from the device tree
> > "current-speed".
> > 
> > Note that the driver uses the generic GNSS serial implementation and
> > therefore essentially only manages power abstracted into three power
> > states: ACTIVE, STANDBY, and OFF.
> > 
> > For mediatek receivers with a main supply and no enable-gpios, this simply
> > means that the main supply is disabled in STANDBY and OFF (the optional
> > backup supply is kept enabled while the driver is bound).
> > 
> > Note that the timepulse-support is left unimplemented.
> > 
> > Signed-off-by: Loys Ollivier <lollivier@...libre.com>

> > +static int mtk_set_active(struct gnss_serial *gserial)
> > +{
> > +	struct mtk_data *data = gnss_serial_get_drvdata(gserial);
> > +	int ret;
> > +
> > +	ret = regulator_enable(data->vcc);
> > +	if (ret)
> > +		return ret;
> > +
> > +	return 0;
> > +}
> 
> Hello
> 
> This could be simplified to return regulator_enable(data->vcc);

Indeed, but I prefer this style which clearly separates the error path
from the success path while making the success return value explicit.

> Furthermore, after this simplification, the function seems useless.

Why do you think so? You still need to retrieve the regulator from the
driver data. Sure, this could be folded into mtk_set_power(), but that
would be less ideal if there are more resources that need to be managed
(e.g. an external lna supply).

Thanks,
Johan