参考:

udelay、mdelay、ndelay、msleep使用比较说明
https://www.cnblogs.com/Ph-one/p/4678361.html

arm体系下的cpu_relax()函数疑惑
http://www.wowotech.net/forum/viewtopic.php?id=21#:~:text=cpu_relax%E5%BF%85%E9%A1%BB%E5%85%B7%E5%A4%87%E4%B8%A4%E4%B8%AA%E5%8A%9F%E8%83%BD%EF%BC%9A%201%E3%80%81%E7%A1%AE%E4%BF%9D%E5%AF%B9flag%E7%9A%84%E8%AE%BF%E9%97%AE%E6%AF%8F%E6%AC%A1%E9%83%BD%E4%BB%8Ememory%E4%B8%AD%E5%8A%A0%E8%BD%BD%EF%BC%8C%E4%B9%9F%E5%B0%B1%E6%98%AFbarrier,%28%29%E5%87%BD%E6%95%B0%E7%9A%84%E4%BD%9C%E7%94%A8%202%E3%80%81%E9%80%9A%E7%9F%A5%E5%BA%95%E5%B1%82CPU%EF%BC%8C%E7%9B%AE%E5%89%8D%E4%BB%A3%E7%A0%81%E6%B2%A1%E6%9C%89%E5%9C%A8%E5%81%9A%E4%BB%80%E4%B9%88%E5%AE%9E%E9%99%85%E6%9C%89%E6%84%8F%E4%B9%89%E7%9A%84%E4%BA%8B%E6%83%85%EF%BC%8C%E5%A6%82%E6%9E%9C%E5%8F%AF%E4%BB%A5%E7%9A%84%E8%AF%9D%EF%BC%8C%E5%88%AB%E8%AE%A9cpu%E5%81%9A%E5%A4%AA%E5%A4%9A%E4%BA%8B%E6%83%85%EF%BC%8C%E7%B3%BB%E7%BB%9F%E7%9A%84%E8%B5%84%E6%BA%90%E5%B0%BD%E9%87%8F%E8%AE%A9%E7%BB%99%E5%85%B6%E4%BB%96%E7%9A%84cpu%E3%80%82

1. 增加头文件 #include <asm/ptrace.h>

2. 在需要打印的地方增加语句 dump_stack();

参考: https://blog.csdn.net/SweeNeil/article/details/88061381

kernel 通过 drm 向 hdmi 设备进行显示，资料可以参考: https://zhuanlan.zhihu.com/p/59784377 https://zhuanlan.zhihu.com/p/60504398 https://dri.freedesktop.org/docs/drm/gpu/drm-kms.html?highlight=writeback https://www.kernel.org/doc/html/v4.17/gpu/drm-kms.html https://blog.csdn.net/u014674293/article/details/105774238 https://www.cnblogs.com/mao0504/p/5619107.html https://blog.csdn.net/hexiaolong2009/article/details/89810355

调整 hdmi 分辨率: https://forum.khadas.com/t/hdmi-resolutions-testing/618/6

增加分辨率: https://cc.bingj.com/cache.aspx?q=%e5%a6%82%e4%bd%95%e8%ae%a9linux%e5%86%85%e6%a0%b8%e6%94%af%e6%8c%81%e6%9b%b4%e5%a4%9a%e5%88%86%e8%be%a8%e7%8e%87&d=4907167835104881&mkt=zh-CN&setlang=zh-CN&w=UBOysQ8Kvqy3hdq6jwa-IuOL_R-qi-XU