On Wed, Sep 11, 2024 at 07:57:17PM +0530, Ayush Singh wrote: > Hello all, > > This is an attempt to add MikroBUS addon support using the approach > described by Grove connector patch series [0]. > > The patch series tests out 2 addon boards + pwm and GPIO on the MikroBUS > connector. The boards used are GPS3 Click (for UART) [1] and Weather > Click (for I2C) [2]. Additionally, I have tested relative GPIO numbering > using devicetree nexus nodes [3]. > > The patch series does not attempt to do any dynamic discovery for 1-wire > eeprom MikroBUS addon boards, nor does it provide any sysfs entry for > board addition/removal. The connector driver might include them after > the basic support is ironed out, but the existing patches for dynamic > overlays work fine. > > The patch series has been tested on BeaglePlay [4]. > > I will now go over individual parts of the patch series, but for a > better picture of the approach, it would be best to checkout [0] first. > > MikroBUS connector driver > ------------------------- > > Just a stub platform driver for now. Will be extended in the future for > dynamic board discovery using 1-wire eeprom present in some MikroBUS > addon boards. > > While it is a stub driver, disabling it will make the GPIO connector > nexus node unreachable (any driver attempting to use it will enter > differed probing). So it is required. > > MikroBUS connector Devicetree > ------------------------------ > > The connector devicetree defines the MikroBUS GPIO nexus node. This > allows using pin numbering relative to MikroBUS connector pins in the > addon boards overlay. Currently, the patch uses a clockwise numbering: > > 0: PWM > 1: INT > 2: RX > 3: TX > 4: SCL > 5: SDA > 6: MOSI > 7: MISO > 8: SCK > 9: CS > 10: RST > 11: AN > > Additionally, in case PWM pin is not using channel 0, a nexus node for pwm > should also be used and go in the connector devicetree. > > MikroBUS connector symbols overlay > ---------------------------------- > > To make an overlay generic we need a standard name scheme which we > use across base boards. For the connector pins the pinmux phandle > shall be: > > <connector-name>_<pin-name>_mux_<pin-function> > > For the parent provider phandle, we use a similar naming scheme: > > <connector-name>_<pin-name>_<pin-function> > > For GPIO controller, I am using `MIKROBUS_GPIO` name since with nexus > nodes, we do not need to define individual pin gpio controllers. > > The string symbols can be replaced with phandles once [5] is accepted. > That will make connector stacking much simpler. > > MikroBUS addon board overlay > ---------------------------- > > The patch puts the addon board overlays in their own directory. I am > using the following naming scheme for MikroBUS addon boards: > > <vendor>-<product_id>.dtso > > Mikroe [6] lists this for all boards in their website, but I am not sure > if other vendors have a product_id. > > This naming also makes future dynamic discovery easier, since click id > spec [7] contains vendor_id and product_id in the header. > > Usage > ----- > > So what does this all look like? Let's take an example of a BeaglePlay > with one MikroBUS connectors for which we have physically attached a > Wather click module to the first connector. Doing ahead of time > command-line DT overlay application: > > ./fdtoverlay \ > -o output.dtb \ > -i k3-am625-beagleplay.dtb \ > k3-am625-beagleplay-mikrobus-connector0.dtbo mikroe-5761.dtbo > > Open Items > ---------- > > - SPI Support: > Currently SPI dt requires `reg` property to specify the > chipselect to use. This, makes the SPI device overlay dependent on the > SPI controller. Thus for SPI support, we need a way to allow defining > SPI chipselect relative to MikroBUS pins, and not the actual device > controller. > > One possible solution is to introduce something like `named-reg` and > allow selecting the chipselect by string array. But this probably > requires more discussion so I have left out SPI support for now. > > NOTE: pins other than the CS MikroBUS pin can be used as chipselect. > See [8]. > > - Controller symbol duplication > The current symbol scheme has multiple symbols for the same underlying > controller (Eg: MIKROBUS_SCL_MUX_I2C_SCL and MIKROBUS_SDA_MUX_I2C_SDA) > point to the same i2c controller. > > I think both of them will always use the same i2c controller, but > maybe there are some exceptions? So I have left it as it is for this > patch series. The same thing also applies to UART and SPI. > > NOTE: with the use of nexus node for GPIO, the GPIO controller symbol > will be the same for all pins. > > - Nexus node dt-bindings > I am not quite sure how to deal with the nexus node properties > (#gpio-cells, gpio-map, gpio-map-mask, gpio-map-pass-thru) since they > seem to conflict with upstream gpio schema (gpio-controller is a > dependency of #gpio-cells). Please submit a fix to dtschema. Either GH PR or patch to devicetree-spec list. Rob
