Greg Kroah-Hartman on Sunday submitted all of the “char/misc” patches for the Linux 6.15 merge window for this random catch-all area of the kernel with small drivers and other random/obscure hardware support.
Introduced by char/misc back in Linux 6.14 was the “faux bus” for simple hardware devices where the drivers had been abusing the platform device interfaces. With Linux 6.15 more of these simple kernel drivers are adapted to using the faux bus for simplifying the driver design/usage rather than continuing to rely on the platform bus interface.
Another new feature of the char/misc pull is introducing support for SPI offloading. The Serial Peripheral Interface (SPI) continues to be of significant use particularly among embedded hardware and various micro-controllers. With SPI offloading it’s possible for the SPI controller to perform transfers without intervention by the CPU. This SPI offloading with bypassing the CPU can be helpful for high speed data acquisition and other use-cases. The SPI offloading support was worked on by engineers from Analog Devices, Bay Libre, and Huawei.
This initial SPI offloading support provides the necessary kernel infrastructure and enables it for the Analog Devices AXI SPI Engine. The AXI SPI Engine can record a series of SPI transactions and then play them back as needed to allow for operations to be taken without CPU intervention.
Greg KH sums up the char/misc pull request for Linux 6.15 as:
“Here is the big set of char, misc, iio, and other smaller driver subsystems for 6.15-rc1. Lots of stuff in here, including:
– loads of IIO changes and driver updates
– counter driver updates
– w1 driver updates
– faux conversions for some drivers that were abusing the platform bus interface
– coresight driver updates
– rust miscdevice binding updates based on real-world-use
– other minor driver updates”
Most interesting is the continued faux bus conversions and this initial SPI offloading with supported hardware while the rest is largely made up of random small changes.
