linux-kernel - [PATCH v3 0/3] i2c: mux: gpio: Add 'settle-time-us' property

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Message-ID: <20240617120818.81237-1-bastien.curutchet@bootlin.com>
Date: Mon, 17 Jun 2024 14:08:15 +0200
From: Bastien Curutchet <bastien.curutchet@...tlin.com>
To: Peter Rosin <peda@...ntia.se>,
	Andi Shyti <andi.shyti@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Peter Korsgaard <peter.korsgaard@...co.com>,
	Wolfram Sang <wsa@...nel.org>
Cc: linux-i2c@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	Herve Codina <herve.codina@...tlin.com>,
	Christopher Cordahi <christophercordahi@...ometrics.ca>,
	Bastien Curutchet <bastien.curutchet@...tlin.com>
Subject: [PATCH v3 0/3] i2c: mux: gpio: Add 'settle-time-us' property

Hi all,

The i2c-gpio-mux can be used to describe a multiplexer built upon
several i2c isolators having an enable pin (such as LTC4310):

 +---------------+                     +------+  +------+
 | +-----------+ |                     | dev  |  | dev  |
 | | GPIO_EN_A |-|-----------|         +------+  +------+
 | +-----------+ |     +-----+---+         |         |
 |               |  |--| isol. A |---------+---------+
 |     +-----+   |  |  +---------+
 | SOC | I2C |---|--|
 |     +-----+   |  |  +---------+
 |               |  |--| isol. B |------+---------+---------+
 | +-----------+ |     +-----+---+      |         |         |
 | | GPIO_EN_B |-|-----------|      +------+  +------+  +------+
 | +-----------+ |                  | dev  |  | dev  |  | dev  |
 +---------------+                  +------+  +------+  +------+

These isolators often need some time between their enable pin's
assertion and the first i2c transfer. If the first i2c transfer
happens before this enabling time is reached, transfer fails.

There is no available option to configure such a time in the
i2c-gpio-mux driver.

Add a optional property in the bindings called 'transition-delay-us'.
If present, driver waits for this delay every time a new bus is
selected, i.e. before returning from the bus_select() callback.

Changes in v2:
 * Rewrite bindings' commit log
 * Express the 'transition delay' in us instead of ms

Changes in v3:
 * Rename DT property to 'settle-time-us'
 * Use fsleep instead of udelay

[v1] : https://lore.kernel.org/all/20240527113908.127893-1-bastien.curutchet@bootlin.com/
[v2] : https://lore.kernel.org/all/20240529091739.10808-1-bastien.curutchet@bootlin.com/

Bastien Curutchet (3):
  dt-bindings: i2c: gpio: Add 'settle-time-us' property
  i2c: mux: gpio: Re-order #include to match alphabetic order
  i2c: mux: gpio: Add support for the 'settle-time-us' property

 .../devicetree/bindings/i2c/i2c-mux-gpio.yaml      |  3 +++
 drivers/i2c/muxes/i2c-mux-gpio.c                   | 14 ++++++++++----
 include/linux/platform_data/i2c-mux-gpio.h         |  2 ++
 3 files changed, 15 insertions(+), 4 deletions(-)

-- 
2.45.0