Re: Re: Re: [PATCH 07/19] media: i2c: imx290: Support variable-sized registers

Laurent Pinchart
2022-08-23T01:08:34Z

Hi Alexander,

On Mon, Jul 25, 2022 at 08:49:40AM +0200, Alexander Stein wrote:
> Am Sonntag, 24. Juli 2022, 01:06:29 CEST schrieb Laurent Pinchart:
> > On Fri, Jul 22, 2022 at 05:37:53PM +0300, Sakari Ailus wrote:
> > > On Thu, Jul 21, 2022 at 01:43:54PM +0200, Alexander Stein wrote:
> > > ...
> > >
> > > > Nice the following snippet does the trick already:
> > > > ---8<---
> > > > --- a/drivers/media/i2c/imx290.c
> > > > +++ b/drivers/media/i2c/imx290.c
> > > > @@ -221,6 +221,7 @@ static const struct imx290_pixfmt imx290_formats[] =
> > > > {
> > > > static const struct regmap_config imx290_regmap_config = {
> > > > .reg_bits = 16,
> > > > .val_bits = 8,
> > > > + .use_single_read = true,
> > > > };
> > > >
> > > > static const char * const imx290_test_pattern_menu[] = {
> > > >
> > > > ---8<---
> > > >
> > > > As this affects the VC OV9281 as well, any suggestions for a common
> > > > property?
> > >
> > > If there's a 1:1 I²C mux in there between the host and the sensor, should
> > > it be in DT as well? I'm not entirely certain it's necessary.
> >
> > The microcontroller also the sensor clock and power supplies, so it has
> > to be modelled in DT in any case. I was trying to avoid exposing it as
> > an I2C mux, but maybe we'll have to bite the bullet...
>
> What is the benefit about exposing a I2C mux? The needed regmap config option
> is configured completely independent to this.

If the I2C mux in the camera module messes up I2C transfers, the related
quirks need to be handled somewhere, and a specific mux driver device in
DT could be a good place to report that. There may be other options
though.

> > I've implement support for two camera modules from Vision Components but
> > haven't submitted patches yet. See [1] and [2] for DT examples and [3]
> > for the driver that handles the microcontroller.
> >
> > Note that one purpose of the microcontroller is to configure the sensor
> > automatically. It can be queried through I2C for a list of supported
> > modes, and it can also reconfigure the sensor fully when a mode is
> > selected. This is meant to enable development of a single driver that
> > will cover all modules, regardless of which camera sensor it integrates.
> > I'm not sure what words you will use to voice your opinion on this
> > design, but I think I already agree :-)
> >
> > [1] https://gitlab.com/ideasonboard/nxp/linux/-/blob/pinchartl/v5.19/dev/isp/next/arch/arm64/boot/dts/freescale/imx8mp-maivin-csi1-imx296.dts
> > [2] https://gitlab.com/ideasonboard/nxp/linux/-/blob/pinchartl/v5.19/dev/isp/next/arch/arm64/boot/dts/freescale/imx8mp-maivin-csi1-imx327.dts
> > [3] https://gitlab.com/ideasonboard/nxp/linux/-/blob/pinchartl/v5.19/dev/isp/next/drivers/media/i2c/vc-mipi.c
> >
> > > The property could be called e.g. "single-octet-read". I think this should
> > > probably be documented in I²C bindings (or even regmap).
> >
> > I like the idea of making it a DT property global to all I2C devices. It
> > should ideally be parsed by the I2C core or by regmap.
>
> I agree with adding this as a regmap option, like 'big-endian' & friends, but
> not so much for I2C core. IMHO the core should only be interested in handling
> messages and transfers. Setting up those correctly is a matter for drivers
> (which in turn use regmap).

I don't want to polute a large number of sensor drivers because of
questionable design decisions of a particular module vendor. This type
of quirk needs to be handled outside of the sensor driver.

--
Regards,

Laurent Pinchart