Raspberry Pi AXI PMU Driver Under Review For The Mainline Linux Kernel

One of the Raspberry Pi device drivers that has remained elusive from the mainline Linux kernel has been for the performance monitoring unit (PMU) for the Broadcom AXI on all Raspberry Pi 1 through Raspberry Pi 5 models. Thanks to the work of a Google engineer, there is a new effort working to get a mainline Linux driver for the Raspberry Pi AXI PMU. Ian Rogers of Google has been working to address the lack of a Linux perf-compatible PMU driver for the performance counters exposed by the Broadcom AXI on Raspberry Pi devices. There are out-of-tree drivers using cusotm DebugFS nodes and the like while Rogers is working to get a mainline-friendly driver that could be upstreamed. The driver patches posted today provide standard Linux perf subsystem integration, expose uncore events via /sys/bus/event_source/devices/rpi_axi_pmu/, supports CPU hot plugging, and other features. This driver support has been worked on for the Broadcom BCM2835-BCM2711 used by the Raspberry Pi 1 through Raspberry Pi 4. There is further work on the BCM2712 with the Raspberry Pi 5 to also expose additional performance monitors around the PCIe RP1 Southbridge links, HEVC decoder, display engine, DSU L3 interconnect monitoring. Those interested in accessing the PMU metrics on the Raspberry Pi single board computers from the mainline Linux kernel can find the proposed patches on the LKML.