[PATCH 2/2] arm64: dts: rockchip: add RK3588 DP carrier from Theobroma Systems
Heiko Stuebner
heiko at sntech.de
Thu Jul 17 11:40:59 PDT 2025
Hi Quentin,
Am Donnerstag, 17. Juli 2025, 14:21:22 Mitteleuropäische Sommerzeit schrieb Quentin Schulz:
> On 7/16/25 8:50 PM, Heiko Stuebner wrote:
> > From: Heiko Stuebner <heiko.stuebner at cherry.de>
> >
> > The DisplayPort carrier is a very simple baseboard only providing serial,
> > ethernet and a displayport output.
> >
> > But its main functionality is that it routes the Analogix eDP controller
> > to this DisplayPort output, which allows to test that controller simply
> > by hooking it up to a suitable monitor.
> >
> > The Analogix-DP controller supports eDP 1.3 and DP 1.2, so can drive
> > both eDP displays as well as full DP monitors. It does not support DP+
> > so passive DP-to-HDMI adapters won't work.
> >
> > Signed-off-by: Heiko Stuebner <heiko.stuebner at cherry.de>
> > ---
> > +&edp0 {
> > + /*
> > + * Note that this board doesn't respect Q7 standard as Q7 has
> > + * lane 2 of HDMI on the same pin as lane 0 of DP and lane 0 of HDMI
> > + * on lane 2 of DP but this board uses HDMI lane numbering instead of
> > + * DP lane numbering for its DP lanes.
> > + *
> > + * It should be possible to match Q7 standard if required by requesting
> > + * the eDPTX controller to swap lanes with:
> > + *
> > + * data-lanes = <2 1 0 3>;
>
> I don't think that's true currently?
>
> The driver only seems to be supporting swapping the lanes, c.f.
> analogix_dp_lane_swap() which routes it to either 0 1 2 3 or 3 2 1 0 but
> no mix like the one we would need. Also, this function is never called
> with anything but "do not swap" argument. So we would need to fix the
> driver to support that.
>
> Also, this is the kind of information we should have in Tiger DTSI and
> not some "random" baseboard DTS which will actually not make use of it.
> We should have data-lanes = <2 1 0 3>; in Tiger DTSI actually but
> considering 1) the driver doesn't support that, 2) we don't have HW to
> validate it works; I guess we'll just leave it at that.
>
> > + */
> > +
>
> Aren't we missing the data-lanes property here? I don't see a default
> and I would assume we should be providing one?
The analogix-dp controller binding does not specify data-lanes at all
and the current driver also does not read it, or use anything
regarding it.
> Documentation/devicetree/bindings/media/video-interfaces.yaml specifies
> it either starts at 0 or 1, depending if there's a clock lane or not. As
> far as I could tell, DP has 4 data lanes and the AUX lane as well, but
> nothing clock-specific so I assume starting at 0 would be correct?
Looks like it. I looked at the vendor-kernel which does allow data-lane
settings and specifies the default as <0 1 2 3> .
So for now, I'll just drop the comment.
> On a side note, is the audio output on eDP TX controller already
> supported like on HDMI? If so, we should add the edp0-sound node like in
> our downstream fork. But looking at the driver, I don't think we
> implement any dp_audio_* callbacks from drm_bridge_funcs which I assume
> would be the way to implement that.
Heiko
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