Re: [PATCH v2 2/2] phy: mtk-mipi-csi: add driver for CSI phy

[AngeloGioacchino Del Regno]

Il 15/05/23 15:36, Julien Stephan ha scritto:
> On Mon, May 15, 2023 at 02:22:52PM +0200, AngeloGioacchino Del Regno wrote:
> > Il 15/05/23 11:05, Julien Stephan ha scritto:
>   ..snip..
> > > +	port->is_cdphy = of_property_read_bool(dev->of_node, "mediatek,is_cdphy");
> >
> > This driver doesn't support C-PHY mode, so you either add support for that, or in
> > my opinion you should simply refuse to probe it, as it is *dysfunctional* for the
> > unsupported case (and might even introduce unstabilities).
> >
> > 	/* At the moment, only D-PHY mode is supported */
> > 	if (!port->is_cdphy)
> > 		return -EINVAL;
> >
> > Also, please don't use underscores for devicetree properties: "mediatek,is-cdphy"
> > is fine.
> Hi Angelo,
> You are right this driver does not support C-PHY mode, but some of the
> PHYs themselves support BOTH C-PHY AND D-PHY. The idea of `is_cdphy` variable
> is to know if the CSI port supports BOTH C-PHY AND D-PHY or only DPHY.
> For example mt8365 has 2 PHYs: CSI0 and CSI1. CSI1 support only D-PHY,
> while CSI0 can be configured in C-PHY or D-PHY. Registers for CD-PHY and
> D-PHY are almost identical, except that CD-PHY compatible has some extra
> bitfields to configure properly the mode and the lanes (because supporting
> trios for CD-PHY).
> If C-PHY support is eventually added into the driver, I think we will need
> another variable such as `mode` to know the mode. I was also thinking
> of adding a phy argument to determine if the mode is C-PHY or D-PHY.
>
> So here, I don't want to stop the probe if `is_cdphy` variable is set to
> true. Does it make sense ?

Comments in the code convinced me that the other PHYs providing only C or D PHY
support weren't compatible at all with this driver.

I got it now - but at this point can you please add a comment in the code actually
clarifying that this driver supports both PHYs providing *only* D-PHY and ones
providing selectable C-or-D PHY?

That clarified, it would not make sense to stop probing if it's not a CDPHY because
as you said there might be a D-only PHY that would be actually supported here.

Regards,
Angelo