[PATCH v4 13/13] Docs: iio: Add AD4134

[Marcelo Schmitt <marcelo.schmitt@analog.com>]

Add initial documentation for the ad4134 IIO driver.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
---
Change log v3 -> v4:
- Minor adjust to AD4134 IIO Doc that made the doc 1 line shorter.

 Documentation/iio/ad4134.rst | 127 +++++++++++++++++++++++++++++++++++
 Documentation/iio/index.rst  |   1 +
 MAINTAINERS                  |   1 +
 3 files changed, 129 insertions(+)
 create mode 100644 Documentation/iio/ad4134.rst

diff --git a/Documentation/iio/ad4134.rst b/Documentation/iio/ad4134.rst
new file mode 100644
index 000000000000..c0889a21cd77
--- /dev/null
+++ b/Documentation/iio/ad4134.rst
@@ -0,0 +1,127 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+=============
+AD4134 driver
+=============
+
+Device driver for Analog Devices Inc. AD4134 and similar ADCs.
+
+Supported devices
+=================
+
+* `AD4134 <https://www.analog.com/AD4134>`_
+* `AD7134 <https://www.analog.com/AD7134>`_
+
+Wiring connections
+------------------
+
+AD4134 and similar ADCs can operate in a few different wiring configurations.
+Because AD4134 also supports control modes other than through SPI protocol,
+the following pins must be statically set for all of the wiring modes described
+below.
+
++----------------------------+----------------------+--------------------+
+| Pin Function               |         Level        | Description        |
++============================+======================+====================+
+| PIN/SPI                    |         High         | SPI control mode   |
++----------------------------+----------------------+--------------------+
+| MODE                       |         Low          | ASRC slave mode    |
++----------------------------+----------------------+--------------------+
+| DEC0/DCLKI                 |         Low          | DCLK input         |
++----------------------------+----------------------+--------------------+
+| DEC1/DCLKMODE              |         Low          | Gated DCLK         |
++----------------------------+----------------------+--------------------+
+
+Minimum I/O mode
+^^^^^^^^^^^^^^^^
+
+The minimum I/O mode wiring allows AD4134 register and data access with the
+conventional set of SPI bus lines. In this mode, the peripheral CS pin must be
+tied to GND. A possible connection schema that sets AD4134 digital interface for
+minimum I/O mode is::
+
+      +------------+         +-------------+
+      |  AD4134    |         | SPI         |
+      |            |         | Controller  |
+      |       DCLK |<--+     |             |
+      |       SCLK |<--+---- | SCLK        |
+      |        SDI |<--------| SDO         |
+      |        SDO |-------->| SDI         |
+      |        ODR |<--------| GPIO        |
+      |         CS |----+    |             |
+      +------------+    |    +-------------+
+                        V
+                       GND
+
+Set ``adi,spi-mode = "no-cs"`` in device tree to indicate the device is
+connected in minimum I/O wiring configuration.
+
+SPI 4-wire mode - single lane
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The conventional SPI 4-wire configuration except a multiplexer is used to
+select between SDO (for register data) and DOUT0 (for ADC sample data).::
+
+  +-----------------------+                         +-----------------+
+  |         AD4134        |                         | SPI Controller  |
+  |                       |                         |                 |
+  | SPI interface    SCLK |<------------------------| SCLK            |
+  | for register       CS |<------------------------| CS              |
+  | access            SDI |<------------------------| SDO             |
+  |                   SDO |------->|¯¯¯¯\           |                 |
+  |                       |        |MUX  >--------->| SDI             |
+  | Data interface DOUT0  |------->|____/           |                 |
+  | for ADC sample        |          ^              |                 |
+  | data read             |          |              |                 |
+  |                  DCLK |<------------------------| DCLK            |
+  |                   ODR |<----------------+    +->| Offload Trigger |
+  +-----------------------+          |      |    |  +-----------------+
+                                     |      |    +--| PWM1            |
+                                     |      +-------| PWM0            |
+                                     +--------------| GPIO            |
+                                                    +-----------------+
+
+Set ``adi,spi-mode = "4-wire"`` in device tree to indicate the device is
+connected in SPI 4-wire configuration.
+
+For SPI offload operation, a PWM is connected to the ADC ODR pin. The ``pwms``
+firmware property specifies the PWM that is connected to the ADC. The SPI
+offload will have a ``trigger-sources`` property to indicate the SPI offload
+(PWM) trigger source.
+
+To achieve high sample rates while meeting ADC timing requirements, an offset
+must be added between the rising edges of PWM0 and PWM1 to delay the SPI
+transfer until ADC sample data is available. This requires a specialized PWM
+controller that can provide such an offset.  The `AD4134-FMC HDL project`_, for
+example, can be configured to sample AD4134 at high speed sample rates.
+
+.. _AD4134-FMC HDL project: https://analogdevicesinc.github.io/hdl/projects/ad4134_fmc/index.html
+
+SPI 4-wire mode - multi-lane
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Maximum throughput rate can be achieved by reading 4 input lines simultaneously.::
+
+  +-----------------------+                         +-----------------+
+  |         AD4134        |                         | SPI Controller  |
+  |                       |                         |                 |
+  | SPI interface    SCLK |<------------------------| SCLK            |
+  | for register       CS |<------------------------| CS              |
+  | access            SDI |<------------------------| SDO             |
+  |                   SDO |------->|¯¯¯¯\           |                 |
+  |                       |        |MUX  >--------->| SDI0            |
+  | Data interface  DOUT0 |------->|____/           |                 |
+  | for ADC sample        |          ^              |                 |
+  | data read       DOUT1 |------------------------>| SDI1            |
+  |                 DOUT2 |------------------------>| SDI2            |
+  |                 DOUT3 |------------------------>| SDI3            |
+  |                  DCLK |<------------------------| DCLK            |
+  |                   ODR |<----------------+    +->| Offload Trigger |
+  +-----------------------+          |      |    |  +-----------------+
+                                     |      |    +--| PWM1            |
+                                     |      +-------| PWM0            |
+                                     +--------------| GPIO            |
+                                                    +-----------------+
+
+Each of SDI0 to SDI3 connect to a different SPI controller deserializer
+(``spi-rx-bus-width = <1>, <1>, <1>, <1>``).
diff --git a/Documentation/iio/index.rst b/Documentation/iio/index.rst
index d0fb32f4b80f..3a49e08a2366 100644
--- a/Documentation/iio/index.rst
+++ b/Documentation/iio/index.rst
@@ -23,6 +23,7 @@ Industrial I/O Kernel Drivers
    ad4000
    ad4030
    ad4062
+   ad4134
    ad4691
    ad4695
    ad7191
diff --git a/MAINTAINERS b/MAINTAINERS
index 3a2dfd1a4fd8..82a810ac788e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1533,6 +1533,7 @@ L:	linux-iio@vger.kernel.org
 S:	Supported
 W:	https://ez.analog.com/linux-software-drivers
 F:	Documentation/devicetree/bindings/iio/adc/adi,ad4134.yaml
+F:	Documentation/iio/ad4134.rst
 F:	drivers/iio/adc/ad4134.c
 
 ANALOG DEVICES INC AD4170-4 DRIVER
-- 
2.53.0