[PATCH 1/2] dt-bindings: iio: adc: ti,ads1298: add ADS1299 EEG ADC variants

[Md Shofiqul Islam <shofiqtest@gmail.com>]

The ADS1299, ADS1299-4, and ADS1299-6 share the same SPI interface
and register map as the ADS1298 ECG ADC family but are designed for
EEG and biopotential measurement.  Key differences from ADS1298:
- PGA gain up to 24x (vs 12x for ADS1298)
- Internal reference is always 2.4V (no 4V option)

Add compatible strings and update the vref-supply description to
document the ADS1299 reference voltage behaviour.

Signed-off-by: Md Shofiqul Islam <shofiqtest@gmail.com>
---
 .../bindings/iio/adc/ti,ads1298.yaml          | 31 ++++++++++++++++---
 1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
index 71f9f9b745cb..82c5181126df 100644
--- a/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
+++ b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
@@ -4,11 +4,16 @@
 $id: http://devicetree.org/schemas/iio/adc/ti,ads1298.yaml#
 $schema: http://devicetree.org/meta-schemas/core.yaml#
 
-title: Texas Instruments' ads1298 medical ADC chips
+title: Texas Instruments ADS1298/ADS1299 biopotential ADC chips
 
 description: |
-  Datasheet at: https://www.ti.com/product/ADS1298
-  Bindings for this chip aren't complete.
+  ADS1298/ADS1298R: 8-channel, 24-bit ECG ADC.
+  Datasheet: https://www.ti.com/product/ADS1298
+
+  ADS1299/ADS1299-4/ADS1299-6: 8/4/6-channel, 24-bit EEG/biopotential ADC.
+  Identical SPI interface and register map to the ADS1298 family, but with
+  a higher maximum PGA gain (24x vs 12x) and fixed 2.4V internal reference.
+  Datasheet: https://www.ti.com/product/ADS1299
 
 maintainers:
   - Mike Looijmans <mike.looijmans@topic.nl>
@@ -17,6 +22,9 @@ properties:
   compatible:
     enum:
       - ti,ads1298
+      - ti,ads1299
+      - ti,ads1299-4
+      - ti,ads1299-6
 
   reg:
     maxItems: 1
@@ -33,8 +41,10 @@ properties:
 
   vref-supply:
     description:
-      Optional reference voltage. If omitted, internal reference is used,
-      which is 2.4V when analog supply is below 4.4V, 4V otherwise.
+      Optional reference voltage. If omitted, internal reference is used.
+      For ADS1298, the internal reference is 2.4V when analog supply is
+      below 4.4V, 4V otherwise. For ADS1299, the internal reference is
+      always 2.4V.
 
   clocks:
     description: Optional 2.048 MHz external source clock on CLK pin
@@ -75,5 +85,16 @@ examples:
           spi-max-frequency = <20000000>;
           spi-cpha;
         };
+
+        adc@2 {
+          reg = <2>;
+          compatible = "ti,ads1299";
+          label = "ads1299-1-eeg";
+          avdd-supply = <&reg_iso_5v_a>;
+          interrupt-parent = <&gpio0>;
+          interrupts = <79 IRQ_TYPE_EDGE_FALLING>;
+          spi-max-frequency = <20000000>;
+          spi-cpha;
+        };
     };
 ...
-- 
2.51.1