linux-kernel - [PATCH RFC v2 7/8] dt-bindings: iio: adc: adi,ad7944: add SPI offload properties

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Message-ID: <20240510-dlech-mainline-spi-engine-offload-2-v2-7-8707a870c435@baylibre.com>
Date: Fri, 10 May 2024 19:44:30 -0500
From: David Lechner <dlechner@...libre.com>
To: Mark Brown <broonie@...nel.org>,
	Jonathan Cameron <jic23@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Nuno Sá <nuno.sa@...log.com>
Cc: David Lechner <dlechner@...libre.com>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	David Jander <david@...tonic.nl>,
	Martin Sperl <kernel@...tin.sperl.org>,
	linux-spi@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org
Subject: [PATCH RFC v2 7/8] dt-bindings: iio: adc: adi,ad7944: add SPI offload properties

To enable capturing data at high rates, the AD7944 is frequently used
with the AXI SPI Engine IP core. This patch adds the properties needed
to describe the SPI offload configuration in the device tree.

The clock trigger and DMA buffer for rx data are external to the SPI
controller and specific to the application so the are included in the
peripheral bindings.

Signed-off-by: David Lechner <dlechner@...libre.com>
---

v2 changes:

This is a new patch that partially replaces "dt-bindings: iio: offload:
add binding for PWM/DMA triggered buffer".

In the previous review, it was suggested that having a separate binding
and object node for the offload was overcomplicated. So instead this
opts to use the proposed standard spi-offloads property as a flag to
allow the SPI periperhal node require additional properties that are
resources that are physically connected to the SPI offload.

On a whim, I also changed pwms to clocks in the binding. The thinking
being that we only care about the frequency (it determines the sample
rate) so a clock made more sense and might allow more flexibility in
the future. But since the actual hardware we have is a PWM, we would
have to use "pwm-clock" in the devicetree to make the PWM act as a
clock. But it turns out that the pwm-clock driver does not support
setting the frequency, so we would have to do more work to actually
be able to use this binding in practice.
---
 .../devicetree/bindings/iio/adc/adi,ad7944.yaml    | 58 ++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad7944.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad7944.yaml
index d17d184842d3..5ea12aac9d25 100644
--- a/Documentation/devicetree/bindings/iio/adc/adi,ad7944.yaml
+++ b/Documentation/devicetree/bindings/iio/adc/adi,ad7944.yaml
@@ -129,6 +129,25 @@ properties:
       line goes high while the SDI and CNV lines are high (chain mode),
     maxItems: 1
 
+  # optional SPI offload support for use with AXI SPI Engine
+
+  spi-offloads:
+    maxItems: 1
+
+  dmas:
+    maxItems: 1
+    description: RX DMA Channel for receiving a samples from the SPI offload.
+
+  dma-names:
+    const: rx
+
+  clocks:
+    maxItems: 1
+    description: Clock to trigger the SPI offload for reading a sample.
+
+  clock-names:
+    const: trigger
+
 required:
   - compatible
   - reg
@@ -190,6 +209,23 @@ allOf:
       properties:
         turbo-gpios: false
 
+  # certain properties are for SPI offload use only
+  - if:
+      required:
+        - spi-offloads
+    then:
+      required:
+        - dmas
+        - dma-names
+        - clocks
+        - clock-names
+    else:
+      properties:
+        dmas: false
+        dma-names: false
+        clocks: false
+        clock-names: false
+
 unevaluatedProperties: false
 
 examples:
@@ -211,3 +247,25 @@ examples:
             turbo-gpios = <&gpio 1 GPIO_ACTIVE_HIGH>;
         };
     };
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+        adc@0 {
+            compatible = "adi,ad7944";
+            reg = <0>;
+            spi-cpha;
+            spi-max-frequency = <111111111>;
+            adi,spi-mode = "single";
+            avdd-supply = <&supply_2_5V>;
+            dvdd-supply = <&supply_2_5V>;
+            vio-supply = <&supply_1_8V>;
+            bvdd-supply = <&supply_5V>;
+            spi-offloads = <0>;
+            dmas = <&dma 0>;
+            dma-names = "rx";
+            clocks = <&trigger_clk>;
+            clock-names = "trigger";
+        };
+    };

-- 
2.43.2