Re: [PATCH v1 2/2] phy: phy-cadence-torrent: Use PHY kernel APIs to set PHY attributes

[Tomi Valkeinen]

On 07/05/2020 20:17, Maxime Ripard wrote:

> > Actually, for this particular case, consumer driver will be the Cadence MHDP
> > bridge driver for DisplayPort which is also under review process for
> > upstreaming [1]. So this DRM bridge driver will make use of the PHY APIs
> > phy_get_bus_width() and phy_get_max_link_rate() during execution of probe
> > function to get the number of lanes and maximum link rate supported by Cadence
> > Torrent PHY. This information is required to set the host capabilities in the
> > DRM bridge driver, based on which initial values for DisplayPort link training
> > will be determined.
> >
> > The changes in this PHY patch series are based on suggestions in the review
> > comments in [1] which asks to use kernel PHY APIs to read these properties
> > instead of directly accessing PHY device node. The complete driver and actual
> > use of these APIs can be found in [2]. This is how we are planning to use
> > these APIs.
>
> I haven't really looked into the displayport spec, but I'd assume that there's a
> lot more parameters that would need to be negociated between the phy and the DP
> block? If so, then it would make more sense to follow the path we did for
> MIPI-DSI where the parameters can be negociated through the phy_configure /
> phy_validate interface.

I don't think this is negotiation, but just exposing the (max) capabilities of PHY, inside which the 
configure can work. Maybe all the capabilities could handled with a struct (struct phy_attrs), 
instead of adding separate functions for each, though.

 Tomi

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