Message-ID: <20240807121648.GC8166@pendragon.ideasonboard.com>
Date: Wed, 7 Aug 2024 15:16:48 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Alexander Stein <alexander.stein@...tq-group.com>
Cc: Benjamin Bara <bbara93@...il.com>,
	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>, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Benjamin Bara <benjamin.bara@...data.com>,
	arne.caspari@...imagingsource.com
Subject: Re: [PATCH 2/2] media: i2c: imx290: Check for availability in probe()

On Wed, Aug 07, 2024 at 02:12:04PM +0200, Alexander Stein wrote:
> Am Mittwoch, 7. August 2024, 13:07:24 CEST schrieb Benjamin Bara:
> > On Wed, 7 Aug 2024 at 11:50, Laurent Pinchart wrote:
> > > On Wed, Aug 07, 2024 at 10:47:39AM +0200, Benjamin Bara wrote:
> > > > On Wed, 7 Aug 2024 at 10:33, Alexander Stein wrote:
> > > > > Am Mittwoch, 7. August 2024, 10:10:28 CEST schrieb Benjamin Bara:
> > > > > > Currently, the V4L2 subdevice is also created when the device is not
> > > > > > available/connected. In this case, dmesg shows the following:
> > > > > >
> > > > > > [   10.419510] imx290 7-001a: Error writing reg 0x301c: -6
> > > > > > [   10.428981] imx290 7-001a: Error writing reg 0x3020: -6
> > > > > > [   10.442712] imx290 7-001a: Error writing reg 0x3018: -6
> > > > > > [   10.454018] imx290 7-001a: Error writing reg 0x3020: -6
> > > > > >
> > > > > > which seems to come from imx290_ctrl_update() after the subdev init is
> > > > > > finished. However, as the errors are ignored, the subdev is initialized
> > > > > > but simply does not work. From userspace perspective, there is no
> > > > > > visible difference between a working and not-working subdevice (except
> > > > > > when trying it out or watching for the error message).
> > > > > >
> > > > > > This commit adds a simple availability check before starting with the
> > > > > > subdev initialization to error out instead.
> > > > >
> > > > > There is already a patch reading the ID register at [1]. This also reads the
> > > > > ID register. But I don't have any documentation regarding that register,
> > > > > neither address nor values definitions. If there is known information about
> > > > > that I would prefer reading the ID and compare it to expected values.
> > > >
> > > > Thanks for the link - it seems like Laurent has dropped the patch for
> > > > the more recent kernel versions on their GitLab.
> > >
> > > It was a patch that I wrote as a test, and I decided not to upstream it
> > > as it had limited value to me. The downside with reading registers at
> > > probe time is that you have to power up the sensor. This can have
> > > undesired side effects, such as flashing a privacy LED on at boot time
> > > in devices that have one. There's also the increase in boot time due to
> > > the power up sequence, which one may want to avoid.
> > >
> > > The imx290 driver already powers up the device unconditionally at probe
> > > time, so reading the version register wouldn't be much of an issue I
> > > suppose. I would be fine merging that patch.
> > >
> > > > This was also my initial intention, but similar to you, I don't have a
> > > > docu describing this register, so I am not sure where the info is coming
> > > > from and if it really contains the identification/type info. Probably
> > > > Laurent has more infos on that.
> > >
> > > That's a good question. I don't see a mention of that register in the
> > > IMX290 datasheet I've found online
> > > (https://static6.arrow.com/aropdfconversion/c0c7efde6571c768020a72f59b226308b9669e45/sony_imx290lqr-c_datasheet.pdf).
> > > Looking at the git history, the IMX290_CHIP_ID register macro was
> > > introduced in an unrelated commit, without an explanation. I don't
> > > recall where it comes from, but I don't think I've added it randomly. It
> > > may have come from an out-of-tree driver.
> > 
> > Thanks for the info!
> > 
> > > I don't have an IMX290 plugged in at the moment, what's the value of the
> > > register ?
> > 
> > I currently have an imx462 available, which is not "officially supported" yet,
> > but basically an imx290 derivative. With your patch applied:
> > 
> > [   10.424187] imx290 7-001a: chip ID 0x07d0
> 
> Okay, this is from a imx327lqr:
> 
> [   15.265086] imx290 3-001a: chip ID 0x07d0
> 
> Doesn't look like an ID register to me.

Indeed, it's quite suspicious.

I wonder if we could find a more applicable register. Chip ID registers
are usually located at the beginning or end of the register space, we
could have a look there.

> > > > > [1] https://gitlab.com/ideasonboard/nxp/linux/-/commit/85ce725f1de7c16133bfb92b2ab0d3d84efcdb47
> > > > >
> > > > > > Signed-off-by: Benjamin Bara <benjamin.bara@...data.com>
> > > > > > ---
> > > > > >  drivers/media/i2c/imx290.c | 5 +++++
> > > > > >  1 file changed, 5 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/media/i2c/imx290.c b/drivers/media/i2c/imx290.c
> > > > > > index 4150e6e4b9a6..a86076e42a36 100644
> > > > > > --- a/drivers/media/i2c/imx290.c
> > > > > > +++ b/drivers/media/i2c/imx290.c
> > > > > > @@ -1580,6 +1580,11 @@ 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, NULL, NULL);
> > > > > > +     if (ret)
> > > > > > +             goto err_pm;
> > > > > > +
> > > > > >       /* Initialize the V4L2 subdev. */
> > > > > >       ret = imx290_subdev_init(imx290);
> > > > > >       if (ret)

-- 
Regards,

Laurent Pinchart

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