linux-kernel - [PATCH] dt-bindings: devicetree: explain how to get CS active-high

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Message-ID: <20241211134023.222473-1-ikerpedrosam@gmail.com>
Date: Wed, 11 Dec 2024 14:40:17 +0100
From: Iker Pedrosa <ikerpedrosam@...il.com>
To: linux-kernel@...r.kernel.org
Cc: Iker Pedrosa <ikerpedrosam@...il.com>,
	broonie@...nel.org,
	robh@...nel.org,
	krzk+dt@...nel.org,
	conor+dt@...nel.org,
	linux-spi@...r.kernel.org,
	devicetree@...r.kernel.org,
	javierm@...hat.com
Subject: [PATCH] dt-bindings: devicetree: explain how to get CS active-high

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@...il.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@...04000 {
+        #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