Re: [PATCH v2 05/66] dt-bindings: sun6i-a31-mipi-dphy: Add optional direction property

Paul Kocialkowski
2022-02-11T15:12:39Z

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Hi Rob,

On Fri 11 Feb 22, 09:03, Rob Herring wrote:
> On Sat, Feb 05, 2022 at 07:53:28PM +0100, Paul Kocialkowski wrote:
> > The Allwinner A31 MIPI D-PHY block supports both tx and rx directions,
> > although each instance of the block is meant to be used in one
> > direction only. There will typically be one instance for MIPI DSI and
> > one for MIPI CSI-2 (it seems unlikely to ever see a shared instance).
> >
> > Describe the direction with a new allwinner,direction property.
> > For backwards compatibility, the property is optional and tx mode
> > should be assumed by default.
> >
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> > ---
> > .../bindings/phy/allwinner,sun6i-a31-mipi-dphy.yaml | 12 ++++++++++++
> > 1 file changed, 12 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/phy/allwinner,sun6i-a31-mipi-dphy.yaml b/Documentation/devicetree/bindings/phy/allwinner,sun6i-a31-mipi-dphy.yaml
> > index d0b541a461f3..22636c9fdab8 100644
> > --- a/Documentation/devicetree/bindings/phy/allwinner,sun6i-a31-mipi-dphy.yaml
> > +++ b/Documentation/devicetree/bindings/phy/allwinner,sun6i-a31-mipi-dphy.yaml
> > @@ -37,6 +37,18 @@ properties:
> > resets:
> > maxItems: 1
> >
> > + allwinner,direction:
> > + $ref: '/schemas/types.yaml#/definitions/string'
> > + description: |
> > + Direction of the D-PHY:
> > + - "rx" for receiving (e.g. when used with MIPI CSI-2);
> > + - "tx" for transmitting (e.g. when used with MIPI DSI).
> > +
> > + enum:
> > + - tx
> > + - rx
> > + default: tx
>
> Can you the phy mode to imply the direction?

So there was a first attempt at this which introduced a PHY submode but
it was concluded after discussions that the direction is not really a
mode of operation choice, in the sense that the D-PHY cannot be reconfigured
to behave in Rx or Tx mode: it is instead statically assigned to one role
or the other. This is why it feels more appropriate to describe it in the
device-tree.

See this thread from the previous iteration:
https://patchwork.linuxtv.org/project/linux-media/patch/20210115200141.1397785-3-paul.kocialkowski@bootlin.com/#128800

Cheers,

Paul

--
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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