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

[Richard Leitner <richard.leitner@linux.dev>]

Hi Laurent,

thank you very much for your quick feedback!

On Tue, Jul 21, 2026 at 06:16:14PM +0300, Laurent Pinchart wrote:
> 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.

I'm basically fine with both. Personally I would prefer the first
option, as this would be a generic approach which other devices could also
use. Furthermore it's IMHO the simpler solution. But that's just my 2 cents.

regards;rl

> 
> > > 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@linux.dev>
> > 
> > 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@raspberrypi.com>
> > 
> > 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