linux-kernel - Re: [PATCH v3 6/7] media: i2c: imx290: Check for availability in probe()

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Message-ID: <CAJpcXm7jYNG1rbLOJcbjHZbdbgFC7g5xGuUrTOE5b9-FcZ9xVQ@mail.gmail.com>
Date: Mon, 2 Sep 2024 22:03:39 +0200
From: Benjamin Bara <bbara93@...il.com>
To: Dave Stevenson <dave.stevenson@...pberrypi.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>, 
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, 
	Sakari Ailus <sakari.ailus@...ux.intel.com>, Hans de Goede <hdegoede@...hat.com>, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
	Alexander Stein <alexander.stein@...tq-group.com>, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Benjamin Bara <benjamin.bara@...data.com>
Subject: Re: [PATCH v3 6/7] media: i2c: imx290: Check for availability in probe()

Hi Dave!

On Mon, 2 Sept 2024 at 20:22, Dave Stevenson
<dave.stevenson@...pberrypi.com> wrote:
> On Mon, 2 Sept 2024 at 16:58, <bbara93@...il.com> wrote:
> >
> > From: Benjamin Bara <benjamin.bara@...data.com>
> >
> > Currently, the V4L2 subdevice is also created when the device is not
> > available/connected. From userspace perspective, there is no visible
> > difference between a working and not-working subdevice (except when
> > trying it out).
> >
> > This commit adds a simple availability check before starting with the
> > subdev initialization to error out instead.
> >
> > Signed-off-by: Benjamin Bara <benjamin.bara@...data.com>
> > ---
> > Changes since v2:
> > - the new 1/8 is split out
> > - use dev_err_probe() (thx Laurent)
> > ---
> >  drivers/media/i2c/imx290.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/drivers/media/i2c/imx290.c b/drivers/media/i2c/imx290.c
> > index 9610e9fd2059..6b292bbb0856 100644
> > --- a/drivers/media/i2c/imx290.c
> > +++ b/drivers/media/i2c/imx290.c
> > @@ -1571,6 +1571,7 @@ static int imx290_probe(struct i2c_client *client)
> >  {
> >         struct device *dev = &client->dev;
> >         struct imx290 *imx290;
> > +       u64 val;
> >         int ret;
> >
> >         imx290 = devm_kzalloc(dev, sizeof(*imx290), GFP_KERNEL);
> > @@ -1631,6 +1632,17 @@ static int imx290_probe(struct i2c_client *client)
> >         pm_runtime_set_autosuspend_delay(dev, 1000);
> >         pm_runtime_use_autosuspend(dev);
> >
> > +       /* Make sure the sensor is available before V4L2 subdev init. */
> > +       ret = cci_read(imx290->regmap, IMX290_STANDBY, &val, NULL);
> > +       if (ret) {
> > +               ret = dev_err_probe(dev, -ENODEV, "Failed to detect sensor\n");
> > +               goto err_pm;
> > +       }
> > +       if (val != IMX290_STANDBY_STANDBY) {
>
> As Laurent commented on v2, this is a slightly unsafe check. If the
> device isn't controlled via a regulator then there's no guarantee that
> the sensor will be in standby.
> The cci_read call will already have returned an error if the sensor
> isn't present which will be 99.999% of the error cases.
>
> If you want to catch the case where it's not in standby, why not put
> it into standby as a recovery mechanism. It'd be a better user
> experience than just bombing out of the probe.

Thanks for the idea - no idea why it didn't come to my mind. I would
also prefer setting STANDBY instead of reading the value.

Kind regards
Benjamin

>   Dave
>
> > +               ret = dev_err_probe(dev, -ENODEV, "Sensor is not in standby\n");
> > +               goto err_pm;
> > +       }
> > +
> >         /* Initialize the V4L2 subdev. */
> >         ret = imx290_subdev_init(imx290);
> >         if (ret)
> >
> > --
> > 2.46.0
> >
> >