Re: [PATCH v5 1/7] dt-bindings: connector: Add mikrobus-connector

Ayush Singh <ayush@xxxxxxxxxxxxxxx> · Tue, 2 Jul 2024 20:44:26 +0530

On 6/28/24 21:58, Rob Herring wrote:

On Thu, Jun 27, 2024 at 09:56:11PM +0530, Ayush Singh wrote:
Add DT bindings for mikroBUS interface. MikroBUS is an open standard
developed by MikroElektronika for connecting add-on boards to
microcontrollers or microprocessors.

mikroBUS is a connector and does not have a controller. Instead the
software is responsible for identification of board and setting up uart,
spi, i2c, pwm and other buses. Additionally, some new mikroBUS boards
contain 1-wire EEPROM that contains a manifest to describe the addon
board to provide plug and play capabilities.

A mikroBUS addon board is free to leave some of the pins unused which
are marked as NC or Not Connected.

Some of the pins might need to be configured as GPIOs deviating from their
reserved purposes Eg: SHT15 Click where the SCL and SDA Pins need to be
configured as GPIOs for the driver (drivers/hwmon/sht15.c) to work.

For some add-on boards the driver may not take care of some additional
signals like reset/wake-up/other. Eg: ENC28J60 click where the reset line
(RST pin on the mikrobus port) needs to be pulled high.

Some SPI addon boards use other pins like RST, AN etc as chipselect (eg.
SPI Extend Click). Thus, `spi-cs` and `spi-cs-names` property is added
to allow mikroBUS addon board to specify chipselect by name.

Here's the list of pins in mikroBUS connector:
AN - Analog
RST - Reset
CS - SPI Chip Select
SCK - SPI Clock
MISO - SPI Master Input Slave Output
MOSI - SPI Master Output Slave Input
+3.3V - VCC-3.3V power
GND - Reference Ground
PWM - PWM output
INT - Hardware Interrupt
RX - UART Receive
TX - UART Transmit
SCL - I2C Clock
SDA - I2C Data
+5V - VCC-5V power
GND - Reference Ground

Link: https://www.mikroe.com/mikrobus
Link:
https://download.mikroe.com/documents/standards/mikrobus/mikrobus-standard-specification-v200.pdf
mikroBUS specification
Link: https://www.mikroe.com/sht1x-click SHT15 Click
Link: https://www.mikroe.com/eth-click ENC28J60 Click
Link: https://www.mikroe.com/spi-extend-click SPI Extend Click

Co-developed-by: Vaishnav M A <vaishnav@xxxxxxxxxxxxxxx>
Signed-off-by: Vaishnav M A <vaishnav@xxxxxxxxxxxxxxx>
Signed-off-by: Ayush Singh <ayush@xxxxxxxxxxxxxxx>
---
  .../bindings/connector/mikrobus-connector.yaml     | 107 +++++++++++++++++++++
  MAINTAINERS                                        |   6 ++
  2 files changed, 113 insertions(+)

diff --git a/Documentation/devicetree/bindings/connector/mikrobus-connector.yaml b/Documentation/devicetree/bindings/connector/mikrobus-connector.yaml
new file mode 100644
index 000000000000..033479f8604f
--- /dev/null
+++ b/Documentation/devicetree/bindings/connector/mikrobus-connector.yaml
@@ -0,0 +1,107 @@
+# SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/connector/mikrobus-connector.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: mikroBUS add-on board connector
+
+maintainers:
+  - Ayush Singh <ayush@xxxxxxxxxxxxxxx>
+
+properties:
+  compatible:
+    const: mikrobus-connector
+
+  pinctrl-0: true
+  pinctrl-1: true
+  pinctrl-2: true
+  pinctrl-3: true
+  pinctrl-4: true
+  pinctrl-5: true
+  pinctrl-6: true
+  pinctrl-7: true
+  pinctrl-8: true
+
+  pinctrl-names:
+    minItems: 1
+    maxItems: 9
+    items:
+      enum: [default, pwm_default, pwm_gpio, uart_default, uart_gpio, i2c_default, i2c_gpio, spi_default,
+             spi_gpio]
Generally, each pinctrl-N is mutually exclusive. It looks like here you
want multiple states active at one time. Does this work?

I see. In mikrobus case, these pinctrl are not mutually exclusive. The 
ones that are mutually exclusive are as follows:

- pwm_default and pwm_gpio

- uart_default and uart_gpio

- i2c_default and i2c_gpio

- spi_default and spi_gpio


It still does lead to 16 combinations so not sure if it is the best 
approach.

+
+  spi-controller:
+    description: spi-controller of mikroBUS SPI pins along with cs pins.
+    $ref: /schemas/types.yaml#/definitions/phandle
+
+  spi-cs:
+    description: spi chip-select corresponding to the chip-selects on the mikrobus socket.
Wrap lines at 80 char.

The array index is the chip-select number on the connector and the
value is the host SPI controller CS numbers? Or the other way around?
This needs a better description.

+    $ref: /schemas/types.yaml#/definitions/uint32-array
Maximum number of entries?

+
+  spi-cs-names:
+    minItems: 1
+    maxItems: 12
+    items:
+      enum: [default, pwm, int, rx, tx, scl, sda, an, rst, sck, cipo, copi]
+
+  i2c-controller:
+    description: i2c controller attached to the mikrobus socket.
+    $ref: /schemas/types.yaml#/definitions/phandle
i2c-bus is the somewhat standard property for this.

Really, I'd expect connectors to look something like this:

connector {
   i2c-0 {
     i2c-bus = <&i2c3>;
     #address-cells = <1>;
     #size-cells = <0>;
     device@12 {
       compatible = "some-i2c-device";
     };
   };
};

That form allows for multiple buses (of the same type or different) on
the connector.

+
+  uart-controller:
+    description: uart controller attached to the mikrobus socket
+    $ref: /schemas/types.yaml#/definitions/phandle
+
+  pwms:
+    description: the pwm-controller corresponding to the mikroBUS PWM pin.
+    maxItems: 1
+
+  mikrobus-gpios:
+    minItems: 1
+    maxItems: 12
+
+  mikrobus-gpio-names:
The GPIO binding does not work this way as the name is in the property.
Either drop if you want to keep the array or you have to do something
like this:

pwm-gpios
int-gpios
rx-gpios

Really, the intention was for connectors to use gpio-map property to
renumber GPIOs relative to the connector.

Can you point me to what you mean by gpio-map property?

+    minItems: 1
+    maxItems: 12
+    items:
+      enum: [pwm, int, rx, tx, scl, sda, an, rst, cs, sck, cipo, copi]
+
+  board:
+    description: board attached to mikrobus connector
+    $ref: /schemas/types.yaml#/definitions/phandle-array
What is this for?

+
+required:
+  - compatible
+  - pinctrl-0
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    mikrobus {
+      compatible = "mikrobus-connector";
+      pinctrl-names = "default", "pwm_default", "pwm_gpio","uart_default", "uart_gpio", "i2c_default",
+                      "i2c_gpio", "spi_default", "spi_gpio";
+      pinctrl-0 = <&P2_03_gpio_input_pin &P1_04_gpio_pin &P1_02_gpio_pin>;
+      pinctrl-1 = <&P2_01_pwm_pin>;
+      pinctrl-2 = <&P2_01_gpio_pin>;
+      pinctrl-3 = <&P2_05_uart_pin &P2_07_uart_pin>;
+      pinctrl-4 = <&P2_05_gpio_pin &P2_07_gpio_pin>;
+      pinctrl-5 = <&P2_09_i2c_pin &P2_11_i2c_pin>;
+      pinctrl-6 = <&P2_09_gpio_pin &P2_11_gpio_pin>;
+      pinctrl-7 = <&P1_12_spi_pin &P1_10_spi_pin &P1_08_spi_sclk_pin &P1_06_spi_cs_pin>;
+      pinctrl-8 = <&P1_12_gpio_pin &P1_10_gpio_pin &P1_08_gpio_pin &P1_06_gpio_pin>;
+      pwms = <&ehrpwm1 0 500000 0>;
+      i2c-controller = <&i2c1>;
+      uart-controller = <&uart1>;
+      spi-controller = <&spi1>;
+      spi-cs = <0 1>;
+      spi-cs-names = "default", "rst";
+      mikrobus-gpios = <&gpio1 18 GPIO_ACTIVE_HIGH>, <&gpio0 23 GPIO_ACTIVE_HIGH>,
+                       <&gpio0 30 GPIO_ACTIVE_HIGH>, <&gpio0 31 GPIO_ACTIVE_HIGH>,
+                       <&gpio0 15 GPIO_ACTIVE_HIGH>, <&gpio0 14 GPIO_ACTIVE_HIGH>,
+                       <&gpio0 4 GPIO_ACTIVE_HIGH>, <&gpio0 3 GPIO_ACTIVE_HIGH>,
+                       <&gpio0 2 GPIO_ACTIVE_HIGH>, <&gpio0 5 GPIO_ACTIVE_HIGH>,
+                       <&gpio2 25 GPIO_ACTIVE_HIGH>, <&gpio2 3 GPIO_ACTIVE_HIGH>;
+    };
diff --git a/MAINTAINERS b/MAINTAINERS
index 807feae089c4..8e4115e93aeb 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15108,6 +15108,12 @@ M:	Oliver Neukum <oliver@xxxxxxxxxx>
  S:	Maintained
  F:	drivers/usb/image/microtek.*
  
+MIKROBUS
+M:	Ayush Singh <ayush@xxxxxxxxxxxxxxx>
+M:	Vaishnav M A <vaishnav@xxxxxxxxxxxxxxx>
+S:	Maintained
+F:	Documentation/devicetree/bindings/connector/mikrobus-connector.yaml
+
  MIKROTIK CRS3XX 98DX3236 BOARD SUPPORT
  M:	Luka Kovacic <luka.kovacic@xxxxxxxxxx>
  M:	Luka Perkov <luka.perkov@xxxxxxxxxx>

--
2.45.2


I am switching to child-node based structure from the next patch since I 
was able to replicate applying board overlay on a generic connector with 
child node.


Ayush Singh








