User:Knuxify/Draft:Qualcomm/Adding a new SoC to mainline Linux

< Qualcomm‎

This guide will cover the process of adding support for a recent (~2020 or newer, todo?) Qualcomm SoC into mainline Linux. Most of the information contained within is also applicable to older chips, though more manual effort may be needed to get these to run.

High-level overview

The basic components of a Qualcomm SoC are:

The GCC, or Global Clock Controller; as the name suggests, it is the primary clock controller for most components.
The other clock controllers: CAMCC, DISPCC, GPUCC and VIDEOCC.
The RPM, or Resource and Power Manager (RPMH or RPM Hardened in SDM845 and later); todo explanation from qcom glossary.
- Under the RPM is the RPM(H)CC (RPM clock controller) and RPM(H)PD (RPM power domains).
QUP, or Qualcomm Universal Peripheral; the part of the SoC that provides I2C or SPI busses, as well as UART.
TLMM (Top Level Mode Multiplexer); provides pinmux and GPIO pins.
Many NOC interconnects (Network on Chip).
A timer and an interrupt controller, both standard ARM parts.

These are just the most low-level components; from there, we can move on to the higher-level ones:

Thermal monitoring sensor
USB host controller and PHY
Display controller and DSI PHY
GPU
etc.

This page will touch on mainline porting of most of these parts.

Finding information about your SoC

In order to begin mainlining your SoC, you need to have the following bits of information:

The codename of your SoC. If you're lucky, it's probably already somewhere out there online. This will be useful when looking things up in the downstream kernel, as it primarily uses the codename, whereas mainline uses the model number. (TODO - we should have a table of SoC codenames somewhere!)
A copy of the downstream kernel; preferably the one for your device, but you can also use the kernel from another device with the same SoC, or - as a last resort - any kernel with the relevant SoC drivers (hint: search by codename).
A copy of the qcom_proprietary_devicetree or similar repo with the DTSI source files (because they're not in the kernel repo for whatever reason...). Search for (codename).dtsi on GitHub and you'll find the right repository eventually.
An extracted DTB from your device. Dump this from a running device using FDT

Porting individual parts

Clock controllers

On recent Qualcomm SoCs, the downstream kernel uses the mainline Qualcomm clock driver with only some vendor-specific quirks. This means that the clock drivers and their relevant headers can pretty much be copied verbatim from downstream, with some slight modifications.