linux-kernel - Re: [PATCH 2/2] media: i2c: imx290: Check for availability in probe()

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Message-ID: <CAJpcXm4CChJUjcZg3DkDb5xJ_ebk7v6VN82BoiF5m27rLgTrfQ@mail.gmail.com>
Date: Wed, 7 Aug 2024 10:50:09 +0200
From: Benjamin Bara <bbara93@...il.com>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: Alexander Stein <alexander.stein@...tq-group.com>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, 
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, Hans de Goede <hdegoede@...hat.com>, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Benjamin Bara <benjamin.bara@...data.com>
Subject: Re: [PATCH 2/2] media: i2c: imx290: Check for availability in probe()

Hi!

On Wed, 7 Aug 2024 at 10:43, Sakari Ailus <sakari.ailus@...ux.intel.com> wrote:
> Hi,
>
> On Wed, Aug 07, 2024 at 10:33:51AM +0200, Alexander Stein wrote:
> > Hi Benjamin,
> >
> > 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.
> >
> > Best regards,
> > Alexander
> >
> > [1] https://gitlab.com/ideasonboard/nxp/linux/-/commit/85ce725f1de7c16133bfb92b2ab0d3d84efcdb47
>
> I'd also prefer reading a register and indeed comparing the read value with
> the expected value.

Sure - I can drop the first patch and check if it contains a "1" (standby).
Probably we learn more about the CHIP_ID, then I can switch to it instead.

Best regards
Benjamin

> --
> Regards,
>
> Sakari Ailus