Add mux controller support for when sdio lines are muxed between a host
and multiple cards.

There are several devices supporting a choice of eMMC or SD on a single
board by both dip switch and gpio, e.g. Renesas RZ/G2L SMARC SoM and
SolidRun RZ/G2L SoM.

In-tree dts for the Renesas boards currently rely on preprocessor macros
to hog gpios and define the card.

By adding mux-states property to sdio controller description, boards can
correctly describe the mux that already exists in hardware - and drivers
can coordinate between mux selection and probing for cards.

Signed-off-by: Josua Mayer <josua@solid-run.com>
---
 Documentation/devicetree/bindings/mmc/renesas,sdhi.yaml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/mmc/renesas,sdhi.yaml b/Documentation/devicetree/bindings/mmc/renesas,sdhi.yaml
index c754ea71f51f7..754ccb1c30efb 100644
--- a/Documentation/devicetree/bindings/mmc/renesas,sdhi.yaml
+++ b/Documentation/devicetree/bindings/mmc/renesas,sdhi.yaml
@@ -106,6 +106,11 @@ properties:
   iommus:
     maxItems: 1
 
+  mux-states:
+    description:
+      mux controller node to route the SDIO signals from SoC to cards.
+    maxItems: 1
+
   power-domains:
     maxItems: 1
 
@@ -275,6 +280,7 @@ examples:
         max-frequency = <195000000>;
         power-domains = <&sysc R8A7790_PD_ALWAYS_ON>;
         resets = <&cpg 314>;
+        mux-states = <&mux 0>;
     };
 
     sdhi1: mmc@ee120000 {

-- 
2.51.0