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Message-ID: <gstohhcdnmnkszk4l2ikd5xiewtotgo5okia62paauj6zpaw7y@4wchyvoynm2p>
Date: Fri, 1 Nov 2024 00:54:49 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Stephen Boyd <swboyd@...omium.org>
Cc: chrome-platform@...ts.linux.dev, linux-kernel@...r.kernel.org,
patches@...ts.linux.dev, devicetree@...r.kernel.org,
Douglas Anderson <dianders@...omium.org>, Pin-yen Lin <treapking@...omium.org>,
Andrzej Hajda <andrzej.hajda@...el.com>, Benson Leung <bleung@...omium.org>,
Conor Dooley <conor+dt@...nel.org>, Daniel Vetter <daniel@...ll.ch>,
David Airlie <airlied@...il.com>, dri-devel@...ts.freedesktop.org,
Guenter Roeck <groeck@...omium.org>, Jernej Skrabec <jernej.skrabec@...il.com>,
Jonas Karlman <jonas@...boo.se>, Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Lee Jones <lee@...nel.org>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
Neil Armstrong <neil.armstrong@...aro.org>, Prashant Malani <pmalani@...omium.org>,
Robert Foss <rfoss@...nel.org>, Rob Herring <robh+dt@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>, Tzung-Bi Shih <tzungbi@...nel.org>,
Alexandre Belloni <alexandre.belloni@...tlin.com>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Daniel Scally <djrscally@...il.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Heikki Krogerus <heikki.krogerus@...ux.intel.com>, Ivan Orlov <ivan.orlov0322@...il.com>,
linux-acpi@...r.kernel.org, linux-usb@...r.kernel.org,
Mika Westerberg <mika.westerberg@...ux.intel.com>, "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
Sakari Ailus <sakari.ailus@...ux.intel.com>, Vinod Koul <vkoul@...nel.org>, Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v4 15/18] dt-bindings: usb: Add ports to
google,cros-ec-typec for DP altmode
On Thu, Oct 31, 2024 at 02:45:29PM -0700, Stephen Boyd wrote:
> Quoting Dmitry Baryshkov (2024-10-31 11:42:36)
> > On Tue, Oct 29, 2024 at 01:15:51PM -0700, Stephen Boyd wrote:
> > > At this point we need to tell the DP bridge, like IT6505, that it's one
> > > or the other output endpoints that it should use, but we haven't
> > > directly connected the usb-c-connector to the output ports of IT6505
> > > because drm_of_find_panel_or_bridge() can't find the parent of the
> > > usb-c-connector if we connect the DP bridge to the usb-c-connector
> > > graphs. We'll need a way for the bridge to know which output port is
> > > connected to a usb-c-connector fwnode. Some sort of API like
> >
> > I think that the final bridge should be the IT6505. It can save you from
> > some troubles, like the inter-bridge lane negotiation. Please remember
> > that using lanes 2-3 as primary lanes doesn't seem to fall into the
> > standard DisplayPort usage. It is documented by USB-C and only because
> > of the orientation switching.
>
> If the final bridge is IT6505 then drm_of_find_panel_or_bridge() isn't
> called and I think we're OK. But then we have to traverse the
> remote-endpoint of the usb-c-connector to IT6505 in displayport.c in the
> Corsola case while knowing to look at the parent of the usb-c-connector
> node and traversing the remote-endpoint to the QMP phy in the Trogdor
> case. The logic in dp_altmode_probe() is like
>
> if (port@...ndpoint@1 exists in usb-c-connector)
> connector_fwnode = port@...ndpoint@...emote-endpoint
> else if (cros-ec-typec/port exists)
> connector_fwnode = cros-ec-typec/port@...ndpoint/remote-endpoint
> else
> original stuff
I'd say, definitely ugh. Maybe we can add the swnode with the
"displayport" property pointing back to the DP bridge / endpoint.
But... read below.
> If we have the crazy three usb-c-connector design it can still work
> because we'd have something like
>
> cros-ec-typec {
> port {
> dp_endpoint: endpoint {
> remote-endpoint = <&dp_ml0_ml1>;
> };
> };
>
> usb-c-connector@0 {
> port@1 {
> endpoint {
> remote-endpoint = <&hub_ss0>;
> };
> // Implicitly dp_ml0_ml1
> };
> };
> usb-c-connector@1 {
> port@1 {
> endpoint@0 {
> remote-endpoint = <&hub_ss1>;
> };
> endpoint@1 {
> remote-endpoint = <&dp_ml2_ml3>;
> };
> };
> };
> usb-c-connector@2 {
> port@1 {
> endpoint {
> remote-endpoint = <&hub_ss2>;
> };
> // Implicitly dp_ml0_ml1
> };
> };
> };
>
> (I like thinking about this 3 connector case because it combines both
> Trogdor and Corsola designs so I can talk about both cases at the same
> time)
>
> I don't know what happens when we have 4 connectors though, with 2 going
> to one pair of lanes and 2 going to the other 2 lanes. Maybe it's better
> to always have a DP input port in cros-ec-typec to avoid this problem
> and map back to the endpoint explicitly.
>
> cros-ec-typec {
> port {
> dp_endpoint0: endpoint@0 {
> remote-endpoint = <&dp_ml0_ml1>;
> };
> dp_endpoint1: endpoint@1 {
> remote-endpoint = <&dp_ml2_ml3>;
> };
> };
>
> usb-c-connector@0 {
> port@1 {
> endpoint@0 {
> remote-endpoint = <&hub_ss0>;
> };
> endpoint@1 {
> remote-endpoint = <&dp_endpoint0>;
> };
> };
> };
> usb-c-connector@1 {
> port@1 {
> endpoint@0 {
> remote-endpoint = <&hub_ss1>;
> };
> endpoint@1 {
> remote-endpoint = <&dp_endpoint1>;
> };
> };
> };
> usb-c-connector@2 {
> port@1 {
> endpoint@0 {
> remote-endpoint = <&hub_ss2>;
> };
> endpoint@1 {
> remote-endpoint = <&dp_endpoint1>;
> };
> };
> };
> };
>
> Or use a displayport property that goes to connector node itself so that
> we don't extend the graph binding of the usb-c-connector.
>
> cros-ec-typec {
> usb-c-connector@0 {
> altmodes {
> displayport {
> connector = <&dp_ml0_ml1>;
I think this has been frowned upon. Not exactly this, but adding the
displayport = <&foo>.
Thus it can only go to the swnode that is generated in software by the
cros-ec driver.
> };
> };
> port@1 {
> endpoint@0 {
> remote-endpoint = <&hub_ss0>;
> };
> };
> };
> usb-c-connector@1 {
> altmodes {
> displayport {
> connector = <&dp_ml2_ml3>;
> };
> };
> port@1 {
> endpoint {
> remote-endpoint = <&hub_ss1>;
> };
> };
> };
> usb-c-connector@2 {
> altmodes {
> displayport {
> connector = <&dp_ml2_ml3>;
> };
> };
> port@1 {
> endpoint {
> remote-endpoint = <&hub_ss2>;
> };
> };
> };
> };
>
> it6505 {
> ports {
> port@1 {
> dp_ml0_ml1: endpoint@0 {
> remote-endpoint = <??>;
> };
> dp_ml2_ml3: endpoint@1 {
> remote-endpoint = <??>;
> };
> };
> };
> };
>
> The logic could look at a node like usb-c-connector@2, find
> altmodes/display node, and look for a 'connector' property that points
> at the endpoint of the last bridge. If we don't use the OF graph binding
> it makes it easier to point at the same endpoint in the QMP phy or the
> IT6505 graph from more than one usb-c-connector. This also makes it very
> clear that we intend to pass that fwnode as the 'connector_fwnode' to
> oob_hotplug_event().
>
> If we want to actually populate the 'remote-endpoint' property of IT6505
> we will need to make a graph in cros-ec-typec.
>
> cros-ec-typec {
> port {
> dp_endpoint0: endpoint@0 {
> remote-endpoint = <&dp_ml0_ml1>;
> };
> dp_endpoint1: endpoint@1 {
> remote-endpoint = <&dp_ml2_ml3>;
> };
> };
> usb-c-connector@0 {
> altmodes {
> displayport {
> connector = <&dp_endpoint0>;
> };
> };
> port@1 {
> endpoint@0 {
> remote-endpoint = <&hub_ss0>;
> };
> };
> };
> usb-c-connector@1 {
> altmodes {
> displayport {
> connector = <&dp_endpoint1>;
> };
> };
> port@1 {
> endpoint {
> remote-endpoint = <&hub_ss1>;
> };
> };
> };
> usb-c-connector@2 {
> altmodes {
> displayport {
> connector = <&dp_endpoint1>;
> };
> };
> port@1 {
> endpoint {
> remote-endpoint = <&hub_ss2>;
> };
> };
> };
> };
>
> it6505 {
> ports {
> port@1 {
> dp_ml0_ml1: endpoint@0 {
> remote-endpoint = <dp_endpoint0>;
> };
> dp_ml2_ml3: endpoint@1 {
> remote-endpoint = <dp_endpoint1>;
> };
> };
> };
> };
>
> and then the logic in displayport.c will have to check if the
> 'connector' property points at a graph endpoint, traverse that to the
> remote-endpoint, and consider that the connector_fwnode.
>
> >
> > Maybe that's just it? Register DP_bridge (or QMP PHY) as
> > orientation-switch? Then you don't need any extra API for the lane
> > mapping? The cross-ec-typec can provide orientation information and the
> > USB-C-aware controller will follow the lane mapping.
>
> I'm not really following but I don't think the DT binding discussed here
> prevents that.
I'm thinking about:
it6505 {
orientation-switch;
ports {
port@1 {
it6505_dp_out: remote-endpoint = <&cros_ec_dp>;
data-lanes = <0 1>;
};
};
};
cros-ec {
port {
cross_ec_dp: remote-endpoint = <&it6505_dp_out>;
};
connector@0 {
reg = <0>;
cros,dp-orientation = "normal";
ports {
// all USB HS and SS ports as usual;
};
};
connector@1 {
reg = <1>;
cros,dp-orientation = "reverse";
ports {
// all USB HS and SS ports as usual;
};
};
connector@2 {
reg = <2>;
cros,dp-orientation = "reverse";
ports {
// all USB HS and SS ports as usual;
};
};
connector@3 {
reg = <3>;
cros,dp-orientation = "normal";
ports {
// all USB HS and SS ports as usual;
};
};
};
The cros-ec registers single drm bridge which will generate HPD events
except on Trogdor, etc. At the same time, cros-ec requests the
typec_switch_get(). When the cros-ec detects that the connector@N it
being used for DP, it just generates corresponding typec_switch_set()
call, setting the orientation of the it6505 (or QMP PHY). The rest can
be handled either by EC's HPD code or by DP's HPD handler, the
orientation should already be a correct one.
So, yes. It requires adding the typec_switch_desc implementation _in_
the it6505 (or in any other component which handles the 0-1 or 2-3
selection). On the other hand as I wrote previously, the 0-1 / 2-3 is
the USB-C functionality, not the DP one.
[...]
>
> >
> > > > > Corsola could work with this design, but we'll need to teach
> > > > > dp_altmode_probe() to look for the drm_bridge elsewhere besides as the
> > > > > parent of the usb-c-connector node. That implies using the 'displayport'
> > > > > property in the cros-ec-typec node or teaching dp_altmode_probe() to
> > > > > look for the port@...ndpoint@1 remote-endpoint handle in the
> > > > > usb-c-connector graph.
> > > > >
> > > > > Assuming the bindings you've presented here are fine and good and I got
> > > > > over the differences between Trogdor and Corsola, then I can make mostly
> > > > > everything work with the drm_connector_oob_hotplug_event() signature
> > > > > change from above and some tweaks to dp_altmode_probe() to look for
> > > > > port@...ndpoint@1 first because that's the "logical" DP input endpoint
> > > > > in the usb-c-connector binding's graph. Great! The final roadblock I'm
> > > > > at is that HPD doesn't work on Trogdor, so I can't signal HPD through
> > > > > the typec framework.
> > > >
> > > > Hmm, I thought that a normal DP's HPD GPIO works on the trogdor. Was I
> > > > misunderstanding it? But then we don't know, which USB-C connector
> > > > triggered the HPD...
> > >
> > > By HPD not working on Trogdor I mean that the EC doesn't tell the kernel
> > > about the state of HPD for a usb-c-connector in software. Instead, HPD
> > > is signaled directly to the DP controller in hardware via a GPIO. It is
> > > as you suspect, we don't know which USB-C connector has HPD unless we
> > > read the mux controlled by the EC and combine that with what the DP
> > > driver knows about the state of the HPD pin.
> >
> > I see. So the HPD event gets delivered to the DP controller, but we
> > really need some API to read the port? If it's not the
> > orientation-switch, of course.
>
> Yes. This is needed to understand what USB type-c connector the DP
> signals should go to. In the case of Corsola/IT6505 it's needed to know
> which two lanes should be sent if both type-c connectors/ports are
> capable of DP altmode. On Corsola, the EC could tell the kernel that
> both ports are in DP altmode but the EC is also controlling the AUX
> channel mux that decides which usb-c-connector type-c port is actually
> displaying DP.
--
With best wishes
Dmitry
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