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

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Message-ID: <CAPY8ntCCCpjohup5Aqrrt6mRXpBukKUFnQWkuwKJ=xJCW=PDog@mail.gmail.com>
Date: Mon, 2 Sep 2024 19:22:43 +0100
From: Dave Stevenson <dave.stevenson@...pberrypi.com>
To: bbara93@...il.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 Benjamin

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.

  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
>
>