GoKawiilPublished: Mon 12 September 2022 In RE.
Those of us who have been trying to make use of the "v10" Mali GPUs from Arm, such as the Mali-G610 in Rockchip's RK3588 will surely have noticed by now the requirement of firmware—kbase requires mali_csffw.bin to be present in one of the firmware directories (such as /lib/firmware ) for the GPU to be usable.
Part 1: What is this firmware and how does it work?
The firmware runs on a microcontroller inside the GPU and handles many tasks required to work the GPU that were previously handled inside the kernel. The MCU ("Microcontroller unit") is, as Alyssa Rosenzweig correctly guessed, a Cortex-M7 (r1p2, with no FPU, ECC cache, nor TCM), which I have found runs off the GPU clock, allowing for an impressive 990 MHz on RK3588. (That speed was measured on my board; maximum clock speeds on the RK3588 vary a bit from chip to chip.)
While the MCU is 32-bit, the GPU supports sixteen eight 48-bit virtual address spaces. So how can it access all of this memory? Arm decided on the obvious method here: simply let the MCU control its own page tables!
Calm down, it isn't quite that bad.
Memory mappings
To access memory, there are three layers that must be navigated:
The MCU's integrated MPU (memory protection unit)
The MCU memory mappings
... continue reading