Re: [PATCH v2 1/2] dt-bindings: media: Add Cadence MIPI-CSI2 RX Device Tree bindings

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Maxime,

On Friday, 25 August 2017 17:44:40 EEST Maxime Ripard wrote:
> On Wed, Aug 23, 2017 at 12:03:32AM +0300, Laurent Pinchart wrote:
> >>>>>> +  - phys: phandle to the external D-PHY
> >>>>>> +  - phy-names: must contain dphy, if the implementation uses an
> >>>>>> +     external D-PHY
> >>>>> 
> >>>>> I would move the last two properties in an optional category as
> >>>>> they're effectively optional. I think you should also explain a bit
> >>>>> more clearly that the phys property must not be present if the phy-
> >>>>> names property is not present.
> >>>> 
> >>>> It's not really optional. The IP has a configuration register that
> >>>> allows you to see if it's been synthesized with or without a PHY. If
> >>>> the right bit is set, that property will be mandatory, if not, it's
> >>>> useless.
> >>> 
> >>> Just to confirm, the PHY is a separate IP core, right ? Is the CSI-2
> >>> receiver input interface different when used with a PHY and when used
> >>> without one ? Could a third-party PHY be used as well ? If so, would
> >>> the PHY synthesis bit be set or not ?
> >> 
> >> The PHY (in our case a D-PHY) is a separate entity, it can be from a 3rd
> >> party as the IP interface is standard, the SoC integrator would set the
> >> bit accordingly based on whether any PHY is present or not. There is also
> >> an option of routing digital output from a CSI-TX to a CSI-RX and in such
> >> case a PHY would not need to be used (as in the case of our current
> >> platform).
> > 
> > OK, thank you for the clarification.
> > 
> > Maxime mentioned that a bit can be read from a register to notify whether
> > a PHY has been synthesized or not. Does it influence the CSI-2 RX input
> > interface at all, or is the CSI-2 RX IP core synthesized the same way
> > regardless of whether a PHY is present or not ?
> 
> So we got an answer to this, and the physical interface remains the
> same.
> 
> However, the PHY bit is set only when there's an internal D-PHY, which
> means we have basically three cases:
>   - No D-PHY at all, D-PHY presence bit not set
>   - Internal D-PHY, D-PHY presence bit set
>   - External D-PHY, D-PHY presence bit not set
> 
> I guess that solves our discussion about whether the phys property
> should be marked optional or not. It should indeed be optional, and
> when it's not there, the D-PHY presence bit will tell whether we have
> to program the internal D-PHY or not.

Is the internal D-PHY programmed through the register space of the CSI2-RX ? 
If so I agree with you.

-- 
Regards,

Laurent Pinchart