The current documentation does not clearly explain how to invert the SPI
CS signal to make it active-high. This makes it very difficult to
understand.

This patch adds a simple explanation on how to set the CS line in
active-high and adds an example to make it easier for users who need
that setup for their SPI peripherals.

Link: https://forums.raspberrypi.com/viewtopic.php?t=378222
Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
---
 .../bindings/spi/spi-controller.yaml          | 24 +++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/Documentation/devicetree/bindings/spi/spi-controller.yaml b/Documentation/devicetree/bindings/spi/spi-controller.yaml
index 093150c0cb87..02dc3e1abcad 100644
--- a/Documentation/devicetree/bindings/spi/spi-controller.yaml
+++ b/Documentation/devicetree/bindings/spi/spi-controller.yaml
@@ -69,6 +69,11 @@ properties:
          Should be generally avoided and be replaced by
          spi-cs-high + ACTIVE_HIGH.
 
+      The simplest way to obtain an active-high CS signal is to configure the
+      controller's cs-gpio property with the ACTIVE_HIGH flag and set the
+      peripheral's spi-cs-high property. See example below for a better
+      understanding.
+
   fifo-depth:
     $ref: /schemas/types.yaml#/definitions/uint32
     description:
@@ -189,3 +194,22 @@ examples:
             stacked-memories = /bits/ 64 <0x10000000 0x10000000>;
         };
     };
+
+  - |
+    spi@20204000 {
+        #address-cells = <1>;
+        #size-cells = <0>;
+        compatible = "brcm,bcm2835-spi";
+        reg = <0x7e204000 0x1000>;
+        interrupts = <2 22>;
+        clocks = <&clk_spi>;
+        cs-gpios = <&gpio 8 GPIO_ACTIVE_HIGH>;
+
+        display@0 {
+            compatible = "sitronix,st7920";
+            spi-max-frequency = <600000>;
+            reg = <0>;
+            spi-cs-high;
+        };
+    };
+
-- 
2.47.1

On Wed, 11 Dec 2024 14:40:17 +0100, Iker Pedrosa wrote:
> The current documentation does not clearly explain how to invert the SPI
> CS signal to make it active-high. This makes it very difficult to
> understand.
> 
> This patch adds a simple explanation on how to set the CS line in
> active-high and adds an example to make it easier for users who need
> that setup for their SPI peripherals.
> 
> Link: https://forums.raspberrypi.com/viewtopic.php?t=378222
> Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
> ---
>  .../bindings/spi/spi-controller.yaml          | 24 +++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 

My bot found errors running 'make dt_binding_check' on your patch:

yamllint warnings/errors:

dtschema/dtc warnings/errors:
Error: Documentation/devicetree/bindings/spi/spi-controller.example.dts:82.33-34 syntax error
FATAL ERROR: Unable to parse input tree
make[2]: *** [scripts/Makefile.dtbs:131: Documentation/devicetree/bindings/spi/spi-controller.example.dtb] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [/builds/robherring/dt-review-ci/linux/Makefile:1506: dt_binding_check] Error 2
make: *** [Makefile:251: __sub-make] Error 2

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/project/devicetree-bindings/patch/20241211134023.222473-1-ikerpedrosam@gmail.com

The base for the series is generally the latest rc1. A different dependency
should be noted in *this* patch.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit after running the above command yourself. Note
that DT_SCHEMA_FILES can be set to your schema file to speed up checking
your schema. However, it must be unset to test all examples with your schema.