MIPI I3C specification published, and new iteration of Linux I3C subsystem

MIPI I3C specification publishedBack in August 2017, Free Electrons contributed to the Linux kernel a patch series adding support for the new MIPI I3C bus, a bus that aims at replacing busses like I2C and SPI, by offering better performance, lower power consumption, and new features like discovery, in-band interrupts and hot join.

At the time of our submission, the I3C specification was closed, but a few days ago, the MIPI Alliance announced that the I3C specification was now publicly available. This is of course very good news as it will allow a much easier and wider adoption of I3C, and it was a somewhat unexpected move since the MIPI Alliance had traditionally kept its specifications only for its members. Hopefully the I3C experience will encourage the MIPI Alliance to follow the same direction for existing or future protocols.

With this announcement from the MIPI Alliance, it was time for us to submit an updated version of our I3C support for the Linux kernel, which Free Electrons engineer Boris Brezillon did on Thursday: [PATCH v2 0/7] Add the I3C subsystem. Compared to the previous version submitted in August, this new version has interesting improvements:

  • A generic infrastructure to support IBIs (in-band interrupts) was added
  • Helpers to support hot-join were added to the core I3C subsystem
  • The Cadence I3C controller driver was improved to support IBIs and hot-join
  • And of course, many of the comments received on the first iteration have been addressed

With the specification now public, we hope to receive useful comments and feedback from the Linux kernel community to improve, and hopefully in the near future, merge the support for the MIPI I3C bus.

Free Electrons proposes an I3C subsystem for the Linux kernel

MIPI I3C fact sheet, from the MIPI I3C white paper
MIPI I3C fact sheet, from the MIPI I3C white paper
At the end of 2016, the MIPI consortium has finalized the first version of its I3C specification, a new communication bus that aims at replacing older busses like I2C or SPI. According to the specification, I3C gets closer to SPI data rate while requiring less pins and adding interesting mechanisms like in-band interrupts, hotplug capability or automatic discovery of devices connected on the bus. In addition, I3C provides backward compatibility with I2C: I3C and legacy I2C devices can be connected on a common bus controlled by an I3C master.

For more details about I3C, we suggest reading the MIPI I3C Whitepaper, as unfortunately MIPI has not publicly released the specifications for this protocol.

For the last few months, Free Electrons engineer Boris Brezillon has been working with Cadence to develop a Linux kernel subsystem to support this new bus, as well as Cadence’s I3C master controller IP. We have now posted the first version of our patch series to the Linux kernel mailing list for review, and we already received a large number of very useful comments from the kernel community.

Free Electrons is proud to be pioneering the support for this new bus in the Linux kernel, and hopes to see other developers contribute to this subsystem in the near future!