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Date: Wed, 5 Aug 2015 00:13:52 -0700
From: Tristan Lelong <tristan@lelong.xyz>
To: Matt Ranostay <mranostay@gmail.com>
Cc: Peter Meerwald <pmeerw@pmeerw.net>,
	Marek =?utf-8?B?VmHFoXV0?= <marex@denx.de>,
	Jonathan Cameron <jic23@kernel.org>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Vladimir Barinov <vladimir.barinov@cogentembedded.com>,
	"linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] iio: proximity: add support for PulsedLight LIDAR
Message-ID: <20150805071352.GA1662@lenderer>
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On Tue, Aug 04, 2015 at 06:45:22PM -0700, Matt Ranostay wrote:
> On Tue, Aug 4, 2015 at 1:35 PM, Tristan Lelong <tristan@lelong.xyz> wrote:
> > On Mon, Aug 03, 2015 at 01:21:08AM -0700, Matt Ranostay wrote:
> >> On Sun, Aug 2, 2015 at 11:48 PM, Peter Meerwald <pmeerw@pmeerw.net> wrote:
> >> > On Sun, 2 Aug 2015, Matt Ranostay wrote:
> >> >
> >> >> +
> >> >> +static int lidar_get_measurement(struct lidar_data *data, u16 *reg)
> >> >> +{
> >> >> +     struct i2c_client *client = data->client;
> >> >> +     int tries = 10;
> >> >> +     int ret;
> >> >> +
> >> >> +     /* start sample */
> >> >> +     ret = lidar_write_control(data, LIDAR_REG_CONTROL_ACQUIRE);
> >> >> +     if (ret < 0) {
> >> >> +             dev_err(&client->dev, "cannot send start measurement command");
> >> >> +             return ret;
> >> >> +     }
> >> >> +
> >> >> +     while (tries--) {
> >> >> +             usleep_range(1000, 2000);
> >> >> +
> >> >> +             ret = lidar_read_byte(data, LIDAR_REG_STATUS);
> >> >> +             if (ret < 0)
> >> >> +                     break;
> >> >> +
> >> >> +             /* return 0 since laser is likely pointed out of range */
> >> >> +             if (ret & LIDAR_REG_STATUS_INVALID) {
> >> >> +                     *reg = 0;
> >> >> +                     ret = 0;
> >> >> +                     break;
> >> >> +             }
> >> >> +
> >> >> +             /* sample ready to read */
> >> >> +             if (!(ret & LIDAR_REG_STATUS_READY)) {
> >> >> +                     ret = lidar_read_measurement(data, reg);
> >> >> +                     break;
> >> >> +             }
> >> >> +     }
> >> >> +
> >> >
> >> > what happens when the timeout occurs?
> >> > no error code is set
> >>
> >> Ah yes it should return an error code.  Would a -EIO be a logical choice?
> >>
> >
> > I would think -ETIMEDOUT to make more sense here.
> 
> Isn't that more applicable for a networking driver to use?

IMHO this error code is generic and should be used when a certain operation doesn't provide any result after a determined period of time. 
In your case, no measurement is available after 10 to 20 msec.

It is used in other iio drivers on similar use cases,
Although it often comes after wait_for_completion_timeout, the scenario is pretty similar:
- start measurement
- wait for measure to be ready

Regards