From e24328974a88aa8541e94e8bb8dfa2ade1b3c45d Mon Sep 17 00:00:00 2001 From: Donggeun Yoo Date: Wed, 2 Sep 2026 00:21:26 +0900 Subject: iio: proximity: vl53l0x-i2c: claim direct mode for raw reads vl53l0x_read_raw() starts a single-shot ranging measurement and reads back the result. Once the triggered buffer is enabled the sensor runs in continuous mode and its data-ready interrupt is routed to the trigger, so a concurrent in_distance_raw read disturbs the streaming setup and never gets its completion, returning -ETIMEDOUT. The original submission claimed direct mode here, but it was dropped during review because the driver had no buffer support at the time [1]. Continuous (buffered) mode was later added without restoring the claim [2], reintroducing the conflict. Reject direct reads while buffered capture is active by claiming direct mode around the measurement, as the vl53l1x sibling already does. Fixes: 762186c6e7b1 ("iio: proximity: vl53l0x-i2c: Added continuous mode support") Link: https://lore.kernel.org/linux-iio/20180911160300.GA9212@himanshu-Vostro-3559/ [1] Link: https://lore.kernel.org/linux-iio/20240909101508.263085-3-abhashkumarjha123@gmail.com/ [2] Signed-off-by: Donggeun Yoo Cc: stable@vger.kernel.org Signed-off-by: Jonathan Cameron --- Documentation/i2c/summary.rst | 82 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 82 insertions(+) create mode 100644 Documentation/i2c/summary.rst (limited to 'Documentation/i2c/summary.rst') diff --git a/Documentation/i2c/summary.rst b/Documentation/i2c/summary.rst new file mode 100644 index 000000000..579a1c7df --- /dev/null +++ b/Documentation/i2c/summary.rst @@ -0,0 +1,82 @@ +============================= +Introduction to I2C and SMBus +============================= + +I²C (pronounce: I squared C and written I2C in the kernel documentation) is +a protocol developed by Philips. It is a two-wire protocol with variable +speed (typically up to 400 kHz, high speed modes up to 5 MHz). It provides +an inexpensive bus for connecting many types of devices with infrequent or +low bandwidth communications needs. I2C is widely used with embedded +systems. Some systems use variants that don't meet branding requirements, +and so are not advertised as being I2C but come under different names, +e.g. TWI (Two Wire Interface), IIC. + +The latest official I2C specification is the `"I²C-bus specification and user +manual" (UM10204) `_ +published by NXP Semiconductors, version 7 as of this writing. + +SMBus (System Management Bus) is based on the I2C protocol, and is mostly +a subset of I2C protocols and signaling. Many I2C devices will work on an +SMBus, but some SMBus protocols add semantics beyond what is required to +achieve I2C branding. Modern PC mainboards rely on SMBus. The most common +devices connected through SMBus are RAM modules configured using I2C EEPROMs, +and hardware monitoring chips. + +Because the SMBus is mostly a subset of the generalized I2C bus, we can +use its protocols on many I2C systems. However, there are systems that don't +meet both SMBus and I2C electrical constraints; and others which can't +implement all the common SMBus protocol semantics or messages. + + +Terminology +=========== + +The I2C bus connects one or more controller chips and one or more target chips. + +.. kernel-figure:: i2c_bus.svg + :alt: Simple I2C bus with one controller and 3 targets + + Simple I2C bus + +A **controller** chip is a node that starts communications with targets. In the +Linux kernel implementation it is also called an "adapter" or "bus". Controller +drivers are usually in the ``drivers/i2c/busses/`` subdirectory. + +An **algorithm** contains general code that can be used to implement a whole +class of I2C controllers. Each specific controller driver either depends on an +algorithm driver in the ``drivers/i2c/algos/`` subdirectory, or includes its +own implementation. + +A **target** chip is a node that responds to communications when addressed by a +controller. In the Linux kernel implementation it is also called a "client". +While targets are usually separate external chips, Linux can also act as a +target (needs hardware support) and respond to another controller on the bus. +This is then called a **local target**. In contrast, an external chip is called +a **remote target**. + +Target drivers are kept in a directory specific to the feature they provide, +for example ``drivers/gpio/`` for GPIO expanders and ``drivers/media/i2c/`` for +video-related chips. + +For the example configuration in the figure above, you will need one driver for +the I2C controller, and drivers for your I2C targets. Usually one driver for +each target. + +Synonyms +-------- + +As mentioned above, the Linux I2C implementation historically uses the terms +"adapter" for controller and "client" for target. A number of data structures +have these synonyms in their name. So, when discussing implementation details, +you should be aware of these terms as well. The official wording is preferred, +though. + +Outdated terminology +-------------------- + +In earlier I2C specifications, controller was named "master" and target was +named "slave". These terms have been obsoleted with v7 of the specification and +their use is also discouraged by the Linux Kernel Code of Conduct. You may +still find them in references to documentation which has not been updated. The +general attitude, however, is to use the inclusive terms: controller and +target. Work to replace the old terminology in the Linux Kernel is on-going. -- cgit v1.3.1