Communication is hard, especially with all the different personalities, languages, and
cultures involved in an international community like this.

– Faith Ekstrand

It is rules and not our individual smarts that keep us from making mistakes.

– Faith Ekstrand

Scent of a woman (1992)

No mistakes in the Tango, not like life. It’s simple, that’s what makes the Tango so great. If you make a mistake, get all tangled up, just Tango on.

Rudy (1993)

Having dreams is what makes life tolerable

The Shawshank Redemption (1994)

Get busy living or get busy dying

Cache

音同 cash, 不管是在硬件还是软件都是影响性能的一个重要因素之一。Cache 无论是 CPU cache 还是 GPU cache 一般都分级， L1，L2, 在 Multi-processor CPU/GPU 架构中， L1 一般是分开的，每个 Processor 有一个自己的 L1 Cache, 而 L2 Cache 是全局的，所有 processors 共享的。

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

1
2
3
4
5
6
7

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

1
2
3
4
5
6
7
8
9
10
11

[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:

1

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

ioctl 的 C 库函数 (Aarch64 实现)：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

	.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)

• KERNELVERSION 是 make kernelrelease 的输出，同时也是 sudo make modules_install 时在 /lib/modules 创建的目录名

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。