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Date: Fri, 2 Sep 2022 07:41:07 +0000
From: Prashant Malani <pmalani@...omium.org>
To: Rob Herring <robh@...nel.org>
Cc: Stephen Boyd <swboyd@...omium.org>,
Pin-yen Lin <treapking@...omium.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Linux USB List <linux-usb@...r.kernel.org>,
Benson Leung <bleung@...omium.org>,
Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com>,
Nícolas F . R . A . Prado
<nfraprado@...labora.com>, Allen Chen <allen.chen@....com.tw>,
Andrzej Hajda <andrzej.hajda@...el.com>,
Daniel Vetter <daniel@...ll.ch>,
David Airlie <airlied@...ux.ie>, devicetree@...r.kernel.org,
dri-devel@...ts.freedesktop.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Hsin-Yi Wang <hsinyi@...omium.org>,
Jernej Skrabec <jernej.skrabec@...il.com>,
Jonas Karlman <jonas@...boo.se>,
José Expósito <jose.exposito89@...il.com>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
Maxime Ripard <maxime@...no.tech>,
Neil Armstrong <narmstrong@...libre.com>,
Robert Foss <robert.foss@...aro.org>,
Sam Ravnborg <sam@...nborg.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
Xin Ji <xji@...logixsemi.com>,
Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCH v5 1/9] dt-bindings: usb: Add Type-C switch binding
Hi Rob,
On Jul 12 11:45, Rob Herring wrote:
>
> That's not the right interpretation. There should not be some Type-C
> specific child mux/switch node because the device has no such h/w within
> it. Assuming all the possibilities Stephen outlined are valid, it's
> clear this lane selection has nothing to do with Type-C. It does have an
> output port for its DP output already and using that to describe the
> connection to DP connector(s) and/or Type-C connector(s) should be
> handled.
> Rob
Below I've listed the proposal binding (for the Type-C connector) along
with 2 sample hardware diagrams and corresponding DT.
The updated binding in usb-c-connector would be as follows:
diff --git a/Documentation/devicetree/bindings/connector/usb-connector.yaml b/Documentation/devicetree/bindings/connector/usb-connector.yaml
index ae515651fc6b..a043b09cb8ec 100644
--- a/Documentation/devicetree/bindings/connector/usb-connector.yaml
+++ b/Documentation/devicetree/bindings/connector/usb-connector.yaml
@@ -183,6 +183,30 @@ properties:
port@1:
$ref: /schemas/graph.yaml#/properties/port
description: Super Speed (SS), present in SS capable connectors.
+ properties:
+ '#address-cells':
+ const: 1
+
+ '#size-cells':
+ const: 0
+
+ patternProperties:
+ "^endpoint@[0-1]$":
+ $ref: /schemas/graph.yaml#/$defs/endpoint-base
+ description:
+ Endpoints for the two SS lanes. endpoint@0 refers to SSTRX1 (A2,A3,B10,B11)
+ and endpoint@1 refers to SSTRX2 (B2,B3,A10,A11).
+ additionalProperties: false
+
+ properties:
+ reg:
+ maxItems: 1
+
+ remote-endpoint: true
+
+ required:
+ - reg
+ - remote-endpoint
port@2:
$ref: /schemas/graph.yaml#/properties/port
Here are 2 examples of how that would look on some existing hardware:
Example 1. 2 usb-c-connectors connecting to 1 drm bridge / DP switch:
Here is the diagram we are using on the MTK platform:
SOC
+---------------------+ C0
| | +----------+ 2 lane +--------+
| | | +---------/---------+ SSTRX1 |
| | | | | |
| MIPI DPI | | | 2 lane | |
| +------------+ ANX 7625 +---/-----+ +----+ SSTRX2 |
| | | | | | +--------+
| | +----------+ | |
+---------------------+ | |
| | +----------+ 2 lane | | C1
| | | +----/----C----+ +--------+
| USB3 HC | 2 lane | | | | SSTRX1 |
| +-----/------+ USB3 HUB | +---------+ |
| (host controller) | | | 2 lane | |
| | | +---------/---------+ SSTRX2 |
+---------------------+ | | | |
+----------+ +--------+
Some platforms use it6505, so that can be swapped in for anx7625
without any change to the rest of the hardware diagram.
>From the above, we can see that it is helpful to describe the
Type-C SS lines as 2 endpoints:
- 1 for SSTX1+SSRX1 (A2,A3 + B10,B11)
- 1 for SSTX2+SSRX2 (B2,B3 + A10, A11)
A device tree for this would look as follows:
// Type-C port driver
ec {
...
cros_ec_typec {
...
usb-c0 {
compatible = "usb-c-connector";
ports {
hs : port@0 {
...
};
ss: port@1 {
reg = <1>;
c0_sstrx1: endpoint@0 {
reg = <0>;
remote-endpoint = <&anx7625_out0>;
};
c0_sstrx2: endpoint@0 {
reg = <0>;
remote-endpoint = <&usb3hub_out0>;
};
};
sbu : port@2 {
...
};
};
};
usb-c1 {
compatible = "usb-c-connector";
ports {
hs : port@0 {
...
};
ss: port@1 {
reg = <1>;
c1_sstrx1: endpoint@0 {
reg = <0>;
remote-endpoint = <&anx7625_out1>;
};
c1_sstrx2: endpoint@0 {
reg = <0>;
remote-endpoint = <&usb3hub_out1>;
};
};
sbu : port@2 {
...
};
};
};
};
};
// DRM bridge / Type-C mode switch
anx_bridge: anx7625@58 {
compatible = "analogix,anx7625";
reg = <0x58>;
...
// Input from DP controller
port@0 {
reg = <0>;
...
};
// Output to Type-C connector / DP panel
port@1 {
reg = <1>;
anx7625_out0: endpoint@0 {
reg = <0>;
mode-switch;
remote-endpoint = <&c0_sstrx1>;
};
anx7625_out1: endpoint@1 {
reg = <1>;
mode-switch;
remote-endpoint = <&c1_sstrx1>;
};
};
};
// USB3 hub
usb3hub: foo_hub {
...
ports@0 {
// End point connected to USB3 host controller on SOC.
};
port@1 {
reg = <1>;
foo_hub_out0: endpoint@0 {
reg = <0>;
mode-switch; ---> See c.) later
remote-endpoint = <&c0_sstrx2>;
};
foo_hub_out1: endpoint@1 {
reg = <1>;
mode-switch;
remote-endpoint = <&c1_sstrx2>;
};
};
};
Notes:
- On the Chrome OS platform, the USB3 Hub is controlled by
the EC, so we don't really need to describe that connection,
but I've added a minimal one here just to show how the graph
connection would work if the HUB was controlled by the SoC.
- The above assumes that other hardware is controlling orientation.
We can add "orientation-switch" drivers along the graph path
if there is other hardware which controls orientation.
Example 2: 1 USB-C connector connected to 1 drm-bridge/ mode-switch
I've tried to use Bjorn's example [1], but I might have made
some mistakes since I don't have access to the schematic.
SoC
+------------------------------------------+
| |
| +---------------+ |
| | | |
| | DP ctrllr | +---------+ | C0
| | +-------+ | | 2 lane +----------+
| +---------------+ | QMP +-----+-----/--------+ SSTRX1 |
| | PHY | | | |
| +-------------+ 2 lane | | | 2 lane | |
| | +----/----+ +-----+-----/--------+ SSTRX2 |
| | dwc3 | +---------+ | | |
| | | | | |
| | | +---------+ | | |
| | +---------+ HS PHY | | HS lanes | |
| +-------------+ | +-----+----/---------+ D +/- |
| | | | +----------+
| +---------+ |
| |
+------------------------------------------+
The DT would look something like this (borrowing from Stephen's example [2]):
qmp {
mode-switch; ----> See b.) later.
orientation-switch;
ports {
qmp_usb_in: port@0 {
reg = <0>;
remote-endpoint = <&usb3_phy_out>;
};
qmp_dp_in: port@1 {
reg = <1>;
remote-endpoint = <&dp_phy_out>;
};
port@2 {
reg = <2>;
qmp_usb_dp_out0: endpoint@0 {
reg = <0>;
remote-endpoint = <&c0_sstrx1>;
};
qmp_usb_dp_out1: endpoint@1 {
reg = <1>;
remote-endpoint = <&c0_sstrx2>;
};
};
};
dp-phy {
ports {
dp_phy_out: port {
remote-endpoint = <&qmp_dp_in>;
};
};
};
dwc3: usb-phy {
ports {
usb3_phy_out: port@0 {
reg = <0>;
remote-endpoint = <&qmp_usb_in>;
};
};
};
glink {
c0: usb-c-connector {
compatible = "usb-c-connector";
ports {
hs: port@0 {
reg = <0>;
endpoint@0 {
reg = <0>;
remote-endpoint = <&hs_phy_out>;
};
};
ss: port@1 {
reg = <1>;
c0_sstrx1: endpoint@0 {
reg = <0>;
remote-endpoint = <&qmp_usb_dp_out0>;
};
c0_sstrx2: endpoint@1 {
reg = <1>;
remote-endpoint = <&qmp_usb_dp_out1>;
};
};
};
};
};
Notes:
a. This proposal doesn't deal with the DRM bridge HPD forwarding; I
believe that is covered by Stephen's example/proposal in [2], and
can be addressed separately. That said, this binding is compatible
with the proposal in [2], that is, make the "mode-switch" driver a
drm-bridge and forward the HPD info to the upstream DRM-bridge (DP controller).
The driver implementing "mode-switch" will be able to do that, since
it gets DP status/attention VDOS with HPD info from the Type-C port driver.
b. If both SSTRX pairs from a connector are routed to the same
hardware block (example 2) then the device would keep "mode-switch"
as a top level property (and the fwnode associated with "mode-switch"
is the drm-bridge device).
c. If SSTRX pairs from 2 connectors are routed to the same
hardware block (example 1), then each end-point which is connected to
the USB-C connector will have a "mode-switch" property in its end-point.
There will be 2 mode switches registered here, and the fwnode for each
"mode-switch" is the end-point node.
b.) and c.) can be handled by Type C mux registration and matching
code. We already have 3 mux devs for each mux [3].
For the single mode-switch case, mux_dev[1] will just refer to the top-level
mode-switch registered by the DRM bridge / switch driver (example 1).
For the 2 mode-switch case, typec_mux_dev[1] will have 2 child
typec_mux_dev's, each of which represents the mode-switches
registered by the DRM bridge / switch driver. Introducing this
indirection means the port driver / alternate mode driver don't
need to care about how the connectors are routed; the framework
will just call the mux_set() function on the mux_dev() or its
children if it has any.
The benefit of this approach is existing bindings (which just
assume 1 endpoint from usb-c-connector/port@1) should continue to
work without any changes.
Why don't we use data lanes for the usb-c-connector
endpoints? I guess we could, but I am not a fan of adding the
extra data-lane parsing logic to the Type-C framework (I
don't think drivers need that level of detail from the connector
binding). And even then, we will still need an extra end-point
if the lanes of the USB-C connector are routed to different hardware blocks.
The Type-C connector spec doesn't specify any alternate modes
with < 1 SSTRX pair, so the most we can ever have (short of a
major change to the spec) is 2 SSTRX end points for a
connector each being routed to different hardware blocks.
Codifying these as endpoint@0 and endpoint@1 in the usb-c-connector
binding seems to line up nicely with this detail of the spec.
Thanks,
-Prashant
[1] https://lore.kernel.org/linux-usb/Yv1y9Wjp16CstJvK@baldur/
[2] https://lore.kernel.org/linux-usb/CAE-0n52-QVeUVCB1qZzPbYyrb1drrbJf6H2DEEW9bOE6mh7egw@mail.gmail.com/
[3] https://elixir.bootlin.com/linux/v6.0-rc3/source/drivers/usb/typec/mux.c#L259
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