LLVM 和 Mesa 简介

LLVM (Low-Level Virtual Machine)

环境准备

WSL2 作为上位机

识别 Windows 11 Host 的 USB Serial Device

分别在 Windows 11 上安装 usbipd-win， 在 WSL2 上安装 user space tools for USB/IP

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Microsoft Windows [版本 10.0.22621.1702]
(c) Microsoft Corporation。保留所有权利。

C:\Windows\System32>usbipd wsl list
BUSID  VID:PID    DEVICE                                                        STATE
1-9    046d:c534  USB 输入设备                                                  Not attached
1-13   04e2:1410  USB 串行设备 (COM4)                                           Not attached

WSL2 Ubuntu-20.04 创建 /dev/ttyUSB0

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[Thu Jun 15 19:19:44 2023] vhci_hcd vhci_hcd.0: pdev(0) rhport(0) sockfd(3)
[Thu Jun 15 19:19:44 2023] vhci_hcd vhci_hcd.0: devid(65546) speed(2) speed_str(full-speed)
[Thu Jun 15 19:19:44 2023] vhci_hcd vhci_hcd.0: Device attached
[Thu Jun 15 19:19:45 2023] vhci_hcd: vhci_device speed not set
[Thu Jun 15 19:19:45 2023] usb 1-1: new full-speed USB device number 2 using vhci_hcd
[Thu Jun 15 19:19:45 2023] vhci_hcd: vhci_device speed not set
[Thu Jun 15 19:19:45 2023] usb 1-1: SetAddress Request (2) to port 0
[Thu Jun 15 19:19:45 2023] usb 1-1: New USB device found, idVendor=04e2, idProduct=1410, bcdDevice= 0.03
[Thu Jun 15 19:19:45 2023] usb 1-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
[Thu Jun 15 19:19:45 2023] xr_serial 1-1:1.0: xr_serial converter detected
[Thu Jun 15 19:19:45 2023] usb 1-1: xr_serial converter now attached to ttyUSB0

Recovery 模式应该连接哪个 Type-C （USB SERIAL) 接口

HiKey970 有两个 Type-C 接口，而且当板子被设置为 Recovery 模式时，两个接口均会被识别为“串口”。在左手边的 (J3101) 是用来访问 Debug UART 的，而在 HDMI 和 USB 中间的那个(J1801)是在 Recovery 模式下使用的。而且这两个接口是两个不同厂家提供的芯片，使用完全不同的内核驱动模块

• 前者(J3101)：
  Bus 001 Device 003: ID 04e2:1410 Exar Corp. XR21V1410 USB-UART IC

• 后者(J1801)：
  Bus 001 Device 002: ID 12d1:3609 Huawei Technologies Co., Ltd. USB SER

显示

flowchart LR
    DPE["Display Engine<br>(display controller)"]
    DSI["Display Serial Interface"]
    HDMI["external HDMI converter"]

    subgraph in-chip
      DPE -- RGB timing --> DSI
    end

    DSI --> HDMI

参考

• HiKey970 官方文档
• DRM driver for HiKey 970
• usbipd-win github issues

系统调用是 Linux 用户态程序与内核通信的接口。 每个特定的文件系统都会在自己的 file_operations 里提供各种文件操作接口，像 .open, .close, .ioctl。系统调用会通过 VFS 的接口调用这些具体的实现，而对于应用程序来说，一般不会直接使用系统调用，而是调用 C 库函数 (C routines).

ioctl 这个系统调用的声明大概是这样:

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COMPAT_SYSCALL_DEFINE3(ioctl, unsigned int, fd, unsigned int, cmd, compat_ulong_t, arg)

ioctl 的 C 库函数 (Aarch64 实现)：

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	.text
ENTRY(__ioctl)
    /* move ioctl syscall number to x8 register */
	mov	x8, #__NR_ioctl
    /* sign extend w0 to x0 */
	sxtw	x0, w0
    /* issue software interrupt to invoke syscall */
	svc	#0x0
    /* add 4095 to x0 and set flags according to result */
	cmn	x0, #4095
    /* if carry bit is set (previous addition carrys out), branch to Lsyscall_error */
	b.cs	.Lsyscall_error
	ret
PSEUDO_END (__ioctl)

/* symbol management, making __ioctl and ioctl effectively the same function */
libc_hidden_def (__ioctl)
weak_alias (__ioctl, ioctl)

CONFIG_DEBUG_FS

如何在 WSL2 上启用 debugfs

确认下内核是否开启了 debugfs

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zcat /proc/config.gz | grep CONFIG_DEBUG_FS

要想使用 debugfs，首先要挂载它到 /sys/kernel/debug

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mount -t debugfs none /sys/kernel/debug/

Gamma LUT property

Gamma LUT (Look-Up Table) is a property that is used to correct the color and brightness of an image or video. Gamma LUT is basically a table of values that is used to map input values to output values, for example, it may map low input values to higher output values to brighten the image.

Gamma LUT is used to adjust the gamma curve of an image or video, which means it can be used to correct the brightness and contrast of an image. This property is commonly used in image and video processing applications, such as photo editing software, video editing software, and color grading tools.

Gamma LUT can also be used to correct color shifts caused by different lighting conditions or camera settings. By adjusting the gamma curve of an image or video, it is possible to create a more natural and accurate representation of the original scene.

Linux 内核的 patch 是以纯文本的邮件形式进行提交和代码走查的，而且 patch 是先到内核子系统 maintainer 维护的 git tree, 再到 Linus Torvalds 的 main tree。本文主要是以一个 patch 提交的实例来记录一下整个过程中的一些具体操作要点，至于 kernel patch 提交的规范和操作细节内核文档 和各种博客文章有很多，这里不再赘述。

来自 ChatGPT 的解释

What is Vulkan ICD?

Vulkan ICD (Installable Client Driver) is a software component that enables the Vulkan API (Application Programming Interface) to interact with the hardware of a computer system. Vulkan is a low-level graphics API developed by the Khronos Group, which provides developers with more control over hardware resources, leading to improved performance and efficiency in graphics-intensive applications such as video games. The Vulkan ICD is responsible for managing the communication between the Vulkan API and the graphics hardware of a system. It is typically provided by the manufacturer of the graphics card as a driver for the system.

Light Display Manager 是一个轻量级的跨桌面环境的 Display Manager, 可以支持多种显示技术，如 X11, Mir, Wayland.

Build

Dependencies

• 开发包依赖

  • libpam0g-dev
  • libgcrypt20-dev
  • libglib2.0-dev
  • libxklavier-dev

• 构建工具依赖

  • intltool
  • yelp-tools
  • gtk-doc-tools

• 安装

Lightdm 可执行程序路径 /usr/sbin/lightdm, 日志默认路径 /var/log/lightdm/lightdm.log. 所以构建时可以使用

• --prefix 指定安装路径 (默认 /usr/local)
• --localstatedir 指定日志路径 (默认 $prefix/var/log/lightdm)
• --sysconfdir 指定 lightdm.conf 路径 （默认 $prefix/etc/lightdm)

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./autogen.sh --prefix=/usr --localstatedir=/var --sysconfdir=/etc --disable-tests
make -j $JOBS
sudo make install

Graphics Boot-up

flowchart TD
    A["systemd"]
    B["/usr/sbin/lightdm"]
    C["`[Seat:*]
        # Dump core
        xserver-command=X -core`"]
    D["`X
        Symbolic link to Xorg`"]

    A -- lightdm.service --> B -- /usr/share/lightdm/lightdm.conf.d/50-xserver-command.conf --> C --> D

P.S. lightdm --show-config 可以显示与 lightdm 相关的配置

Should Know Something About Kernel Building

• 配置内核最简单的方法是 make olddefconfig
• 内核配置保存在 .config
• 内核源码树里包含命令行修改 .config 的脚本 scripts/config
• 内核构建依赖 flex, bison 词法分析程序

Build on Ubuntu 22.04

Environment

Compilation Errors

Build on WSL2

Build Config

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make KCONFIG_CONFIG=Microsoft/config-wsl

Compilation Errors

apt install -y dwarves

这是一个非常常见的依赖问题

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  LD      vmlinux.o
  MODPOST vmlinux.symvers
  MODINFO modules.builtin.modinfo
  GEN     modules.builtin
BTF: .tmp_vmlinux.btf: pahole (pahole) is not available
Failed to generate BTF for vmlinux
Try to disable CONFIG_DEBUG_INFO_BTF
make: *** [Makefile:1218: vmlinux] Error 1

Direct WSL to the new vmlinux

新内核产生

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  AS      arch/x86/boot/header.o
  CC      arch/x86/boot/version.o
  LD      arch/x86/boot/setup.elf
  OBJCOPY arch/x86/boot/setup.bin
  OBJCOPY arch/x86/boot/vmlinux.bin
  BUILD   arch/x86/boot/bzImage
Kernel: arch/x86/boot/bzImage is ready  (#3)
  MODPOST modules-only.symvers
  GEN     Module.symvers

新内核生效

1. mv arch/x86/boot/bzImage /mnt/c/Users/luc/

2. 编辑 /mnt/c/Users/luc/.wslconfig, 添加下面两行

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[wsl2]
kernel=C:\\Users\\luc\\bzImage

NOTE: 如果以上两行添加进 /etc/wsl.conf 文件，不会有任何作用, 因为 /etc/wsl.conf 不支持 wsl2 Section

3. 配置完成后，重启 WSL Ubuntu 20.04, 新编译的内核将生效。不要用 wsl --terminate.

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wsl --shutdown Ubuntu-20.04

打开 CONFIG_DRM_VKMS

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make nconfig

NOTE: 在 WSL 上不能将配置项置为 ‘M’, 而要 ‘Y’

配置更改后重新 make

Testing With IGT on WSL2

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➜  tests git:(master) sudo ./kms_writeback --device "sys:/sys/devices/platform/vkms"
IGT-Version: 1.27.1-g45da871d (x86_64) (Linux: 5.15.90.1-microsoft-standard-WSL2+ x86_64)
(kms_writeback:9671) igt_kms-WARNING: Output Writeback-1 could not be assigned to a pipe
Starting subtest: writeback-pixel-formats
Subtest writeback-pixel-formats: SUCCESS (0.000s)
Starting subtest: writeback-invalid-parameters
Subtest writeback-invalid-parameters: SUCCESS (0.000s)
Starting subtest: writeback-fb-id
Subtest writeback-fb-id: SUCCESS (0.018s)
Starting subtest: writeback-check-output
Subtest writeback-check-output: SUCCESS (0.124s)

• dmesg

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[10893.662944] [IGT] kms_writeback: executing
[10893.673240] [IGT] kms_writeback: starting subtest writeback-pixel-formats
[10893.674026] [IGT] kms_writeback: starting subtest writeback-invalid-parameters
[10893.675055] [IGT] kms_writeback: starting subtest writeback-fb-id
[10893.693563] [IGT] kms_writeback: starting subtest writeback-check-output
[10893.826984] [IGT] kms_writeback: exiting, ret=0