Re: [PATCH v3 1/7] phy: Distinguish between Rx and Tx for MIPI D-PHY with submodes

Pratyush Yadav
2021-08-11T17:36:45Z

On 06/08/21 01:11PM, Paul Kocialkowski wrote:
> Hi,
>
> On Fri 25 Jun 21, 00:11, Pratyush Yadav wrote:
> > From: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> >
> > As some D-PHY controllers support both Rx and Tx mode, we need a way for
> > users to explicitly request one or the other. For instance, Rx mode can
> > be used along with MIPI CSI-2 while Tx mode can be used with MIPI DSI.
> >
> > Introduce new MIPI D-PHY PHY submodes to use with PHY_MODE_MIPI_DPHY.
> > The default (zero value) is kept to Tx so only the rkisp1 driver, which
> > uses D-PHY in Rx mode, needs to be adapted.
>
> After some thinking and discussions, it appears that using the submode is
> probably not the best way to distinguish between rx and tx. This is because
> rx/tx is more of a specification of the hardware component than a run-time
> descision. Indeed the D-PHY blocks are usually dedicated to an associated
> controller (DSI or CSI-2) and thus each instance is either meant for tx or
> rx use.

Ok. IIRC Laurent also brought this point up earlier as well. At that
time I took the allwinner DPHY as an example of a DPHY that can run in
both modes.

The Cadence DPHY also supports both Rx and Tx modes but I don't know if
both can be implemented at the same time, if that would even make any
sense.

>
> As a result I will be using the allwinner,direction string property in
> device-tree instead of the submode, with values of either "rx" or "tx".
> I suppose you can do something similar if you agree it makes more sense.

Wouldn't a different compatible a better idea?

>
> Cheers,
>
> Paul
>
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> > Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
> > ---
> >
> > (no changes since v1)
> >
> > include/linux/phy/phy-mipi-dphy.h | 13 +++++++++++++
> > 1 file changed, 13 insertions(+)
> >
> > diff --git a/include/linux/phy/phy-mipi-dphy.h b/include/linux/phy/phy-mipi-dphy.h
> > index a877ffee845d..0f57ef46a8b5 100644
> > --- a/include/linux/phy/phy-mipi-dphy.h
> > +++ b/include/linux/phy/phy-mipi-dphy.h
> > @@ -6,6 +6,19 @@
> > #ifndef __PHY_MIPI_DPHY_H_
> > #define __PHY_MIPI_DPHY_H_
> >
> > +/**
> > + * enum phy_mipi_dphy_submode - MIPI D-PHY sub-mode
> > + *
> > + * A MIPI D-PHY can be used to transmit or receive data.
> > + * Since some controllers can support both, the direction to enable is specified
> > + * with the PHY sub-mode. Transmit is assumed by default with phy_set_mode.
> > + */
> > +
> > +enum phy_mipi_dphy_submode {
> > + PHY_MIPI_DPHY_SUBMODE_TX = 0,
> > + PHY_MIPI_DPHY_SUBMODE_RX,
> > +};
> > +
> > /**
> > * struct phy_configure_opts_mipi_dphy - MIPI D-PHY configuration set
> > *
> > --
> > 2.30.0
> >
>
> --
> Paul Kocialkowski, Bootlin
> Embedded Linux and kernel engineering
> https://bootlin.com

--
Regards,
Pratyush Yadav
Texas Instruments Inc.