Re: [PATCH 2/2] media: ov9282: enable single-read I2C transactions

[Laurent Pinchart]

On Tue, Jul 21, 2026 at 02:39:46PM +0100, Dave Stevenson wrote:
> On Tue, 21 Jul 2026 at 14:25, Richard Leitner wrote:
> >
> > Some OV9282 camera modules, such as those from Vision Components, fail
> > multi-byte register reads with the default CCI I2C regmap access pattern
> > and only work when single-register read transactions are used. This
> > results in the driver being unable to probe due to a chip id mismatch.
> 
> Those damn stupid Vision Components modules with the MCU that prevents
> you reading registers.

There's good news, the situation is improving with recent modules. We
still have to handle the other ones of course.

> I seem to recall Laurent had a plan for how to handle those without
> having to patch all the drivers, however I can't find that thread
> quickly.

I'm thinking of two options:

- We can introduce a new standard DT property for I2C device that will
  be parsed by regmap or the I2C core directly, and switch to single
  reads.

- We could model the MCU as some sort of I2C mux, sitting in DT between
  the I2C controller and the image sensor, and translate multi-byte
  reads to single-byte reads in that driver.

> > As the driver has no reliable way to identify affected modules enable
> > use_single_read for OV9282 unconditionally when creating the CCI regmap.
> >
> > Tested on an i.M8MP system with OV9282 modules from Vision Components.
> >
> > Signed-off-by: Richard Leitner <richard.leitner@xxxxxxxxx>
> 
> As regmap does provide a simple way to request this behaviour, and the
> only read is the ID register from ov9282_detect, I'll give it an
> 
> Acked-by: Dave Stevenson <dave.stevenson@xxxxxxxxxxxxxxx>
> 
> but it's not an ideal situation. Others can debate the alternative
> approaches for handling VC modules.
> 
> > ---
> >  drivers/media/i2c/ov9282.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/media/i2c/ov9282.c b/drivers/media/i2c/ov9282.c
> > index 5b6f897a74fcd..8267a0a9c6f2d 100644
> > --- a/drivers/media/i2c/ov9282.c
> > +++ b/drivers/media/i2c/ov9282.c
> > @@ -1283,6 +1283,11 @@ static int ov9282_probe(struct i2c_client *client)
> >         struct ov9282 *ov9282;
> >         int ret;
> >
> > +       const struct cci_regmap_config config = {
> > +               .reg_addr_bits = 16,
> > +               .use_single_read = true,
> > +       };
> > +
> >         ov9282 = devm_kzalloc(&client->dev, sizeof(*ov9282), GFP_KERNEL);
> >         if (!ov9282)
> >                 return -ENOMEM;
> > @@ -1301,7 +1306,7 @@ static int ov9282_probe(struct i2c_client *client)
> >                 return ret;
> >         }
> >
> > -       ov9282->regmap = devm_cci_regmap_init_i2c(client, 16);
> > +       ov9282->regmap = devm_cci_regmap_init_i2c_cfg(client, &config);
> >         if (IS_ERR(ov9282->regmap))
> >                 return dev_err_probe(ov9282->dev, PTR_ERR(ov9282->regmap),
> >                                      "Failed to init CCI\n");

-- 
Regards,

Laurent Pinchart