| From: |
| Jonas Jelonek <jelonek.jonas-AT-gmail.com> |
| To: |
| Linus Walleij <linus.walleij-AT-linaro.org>, Bartosz Golaszewski <brgl-AT-bgdev.pl>, Rob Herring <robh-AT-kernel.org>, Krzysztof Kozlowski <krzk+dt-AT-kernel.org>, Conor Dooley <conor+dt-AT-kernel.org> |
| Subject: |
| [RFC PATCH v1 0/2] add support for splitting GPIOs |
| Date: |
| Thu, 09 Oct 2025 22:34:59 +0000 |
| Message-ID: |
| <20251009223501.570949-1-jelonek.jonas@gmail.com> |
| Cc: |
| linux-gpio-AT-vger.kernel.org, devicetree-AT-vger.kernel.org, linux-kernel-AT-vger.kernel.org, Jonas Jelonek <jelonek.jonas-AT-gmail.com> |
| Archive-link: |
| Article |
Hereby I propose a new type of virtual GPIO controller and corresponding
driver for splitting GPIOs using a multiplexer for different usecases.
Existing drivers apparently do not serve the purpose for what I need.
I came across an issue with a switch device from Zyxel which has two
SFP+ cages. Most similar switches either wire up the SFP signals
(RX_LOS, MOD_ABS, TX_FAULT, TX_DISABLE) directly to the SoC (if it has
enough GPIOs) or two a GPIO expander (for which a driver usually
exists). However, Zyxel decided to do it differently in the following
way:
The signals RX_LOS, MOD_ABS and TX_FAULT share a single GPIO line to
the SoC. Which one is actually connected to that GPIO line at a time
is controlled by a separate multiplexer, a GPIO multiplexer in this
case (which uses two other GPIOs). Only the TX_DISABLE is separate.
The SFP core/driver doesn't seem to support such a usecase for now, for
each signal one needs to specify a separate GPIO like:
los-gpio = <&gpio0 0 GPIO_ACTIVE_HIGH>;
mod-def0-gpio = <&gpio0 1 GPIO_ACTIVE_LOW>;
...
But for my device, I actually need to directly specify multiplexing
behavior in the SFP node or provide a mux-controller with 'mux-control'.
To fill this gap, I created a dt-schema and a working driver which
exactly does what is needed. It takes a phandle to a mux-controller and
the 'shared' gpio, and provides several virtual GPIOs based on the
children nodes defined for the gpio-split controller, each with a
mux-state which is used on access.
This virtual gpio-controller can then be referenced in the '-gpio'
properties of the SFP node (or other nodes depending on the usecase) as
usual and do not require any modification to the SFP core/driver.
--
Jonas Jelonek (2):
dt-bindings: gpio: add gpio-split controller
gpio: add gpio-split driver
.../devicetree/bindings/gpio/gpio-split.yaml | 77 +++++++
MAINTAINERS | 6 +
drivers/gpio/Kconfig | 8 +
drivers/gpio/Makefile | 1 +
drivers/gpio/gpio-split.c | 210 ++++++++++++++++++
5 files changed, 302 insertions(+)
create mode 100644 Documentation/devicetree/bindings/gpio/gpio-split.yaml
create mode 100644 drivers/gpio/gpio-split.c
base-commit: bc061143637532c08d9fc657eec93fdc2588068e
--
2.48.1
