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Message-Id: <20240911-mikrobus-dt-v1-0-3ded4dc879e7@beagleboard.org>
Date: Wed, 11 Sep 2024 19:57:17 +0530
From: Ayush Singh <ayush@...gleboard.org>
To: fabien.parent@...aro.org, d-gole@...com, lorforlinux@...gleboard.org,
jkridner@...gleboard.org, robertcnelson@...gleboard.org,
Andrew Davis <afd@...com>, Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>,
Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <benno.lossin@...ton.me>,
Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
Trevor Gross <tmgross@...ch.edu>, Rob Herring <robh@...nel.org>,
Krzysztof Kozlowski <krzk+dt@...nel.org>,
Conor Dooley <conor+dt@...nel.org>, Derek Kiernan <derek.kiernan@....com>,
Dragan Cvetic <dragan.cvetic@....com>, Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Nishanth Menon <nm@...com>,
Vignesh Raghavendra <vigneshr@...com>, Tero Kristo <kristo@...nel.org>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
Ayush Singh <ayush@...gleboard.org>
Subject: [PATCH 0/8] Add generic overlay for MikroBUS addon boards
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).
[0]: https://lore.kernel.org/linux-arm-kernel/20240702164403.29067-1-afd@ti.com/
[1]: https://www.mikroe.com/gps-3-click
[2]: https://www.mikroe.com/weather-click
[3]: https://devicetree-specification.readthedocs.io/en/v0.3/devicetree-basics.html#nexus-nodes-and-specifier-mapping
[4]: https://www.beagleboard.org/boards/beagleplay
[5]: https://lore.kernel.org/r/20240902-symbol-phandle-v1-0-683efb2a944b@beagleboard.org
[6]: https://www.mikroe.com/
[7]: https://github.com/MikroElektronika/click_id
[8]: https://www.mikroe.com/spi-extend-click
Signed-off-by: Ayush Singh <ayush@...gleboard.org>
---
Ayush Singh (7):
dt-bindings: connector: Add MikorBUS connector
mikrobus: Add mikrobus driver
dts: ti: k3-am625-beagleplay: Enable mikroBUS connector
dts: ti: beagleplay: Add mikrobus connector symbols
addon_boards: Add addon_boards plumbing
addon_boards: mikrobus: Add Weather Click
addon_boards: mikrobus: Add GPS3 Click
Fabien Parent (1):
rust: kernel: Add Platform device and driver abstractions
.../bindings/connector/mikrobus-connector.yaml | 40 +++
Kbuild | 1 +
Kconfig | 2 +
MAINTAINERS | 8 +
addon_boards/Kconfig | 16 +
addon_boards/Makefile | 3 +
addon_boards/mikrobus/Makefile | 4 +
addon_boards/mikrobus/mikroe-1714.dtso | 28 ++
addon_boards/mikrobus/mikroe-5761-i2c.dtso | 28 ++
arch/arm64/boot/dts/ti/Makefile | 1 +
.../k3-am625-beagleplay-mikrobus-connector0.dtso | 49 +++
arch/arm64/boot/dts/ti/k3-am625-beagleplay.dts | 53 ++-
drivers/misc/Kconfig | 17 +
drivers/misc/Makefile | 1 +
drivers/misc/mikrobus.rs | 32 ++
rust/bindings/bindings_helper.h | 1 +
rust/kernel/lib.rs | 1 +
rust/kernel/platform.rs | 380 +++++++++++++++++++++
18 files changed, 659 insertions(+), 6 deletions(-)
---
base-commit: 9aaeb87ce1e966169a57f53a02ba05b30880ffb8
change-id: 20240826-mikrobus-dt-52eaaadd0b1f
Best regards,
--
Ayush Singh <ayush@...gleboard.org>
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