[PATCH RFC 09/10] dt-bindings: display: rockchip: dw-dp: fix sound DAI cells

[Sebastian Reichel]

The RK3588 and RK3576 DesignWare DisplayPort controllers both have two
possible DAI interfaces: I2S and S/PDIF. Thus it is needed to have an
argument to select the right interface.

In case of RK3576 this is not enough though. The RK3576 has the same IP
as RK3588, but configured with Multi Stream Transport (MST) enabled for
up to 3 displays and thus has a total of 6 DAI interfaces (I2S and
S/PDIF for each possible stream. Meanwhile the RK3588 does not support
MST and thus has only 2 DAI interfaces.

The binding update right now only supports the simple single stream
transport (SST) setup. To avoid further DT ABI breakage (or complicated
bindings supporting different number of arguments), it's probably a good
idea to take MST into account now even though the upstream Linux driver
does not yet support it.

I see two options:

1. Adding yet another cell, so that we have the following:
   <&dp_ctrl [display_stream] [i2s_or_spdif]>; potentially append
   extra input ports for MST video data to existing ports node
   (e.g. port at 2). I would only handle the sound DAI part in my
   patch and basically use '0' for the display stream and just
   leave the option of using '1' or '2' once MST support is added.

2. The vendor kernel creates a sub-node for each supported display
   stream and puts the ports mapping as well as the DAI reference
   into that. This bundles all information for one display stream
   together, which creates a clean look but the subnode does not
   really describe any real thing in the hardware.

As upstream MST support seems to be quite limited, I wish for some
feedback about the preferred way to handle this.

Signed-off-by: Sebastian Reichel <sebastian.reichel at collabora.com>
---
 .../devicetree/bindings/display/rockchip/rockchip,dw-dp.yaml         | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/devicetree/bindings/display/rockchip/rockchip,dw-dp.yaml b/Documentation/devicetree/bindings/display/rockchip/rockchip,dw-dp.yaml
index 2b0d9e23e943..1303d0e2145a 100644
--- a/Documentation/devicetree/bindings/display/rockchip/rockchip,dw-dp.yaml
+++ b/Documentation/devicetree/bindings/display/rockchip/rockchip,dw-dp.yaml
@@ -83,7 +83,8 @@ properties:
     maxItems: 1
 
   "#sound-dai-cells":
-    const: 0
+    const: 1
+    description: 0 for I2S, 1 for SPDIF
 
 required:
   - compatible
@@ -144,7 +145,7 @@ examples:
         resets = <&cru SRST_DP0>;
         phys = <&usbdp_phy0 PHY_TYPE_DP>;
         power-domains = <&power RK3588_PD_VO0>;
-        #sound-dai-cells = <0>;
+        #sound-dai-cells = <1>;
 
         ports {
           #address-cells = <1>;

-- 
2.53.0