They ignore them, sadly. They did a PR stunt claiming to be open source a while ago, but all they did was release some patches to apply Miui to AOSP if one want

They ignore them, sadly. They did a PR stunt claiming to be open source a while ago, but all they did was release some patches to apply Miui to AOSP if one wanted to do so, but they infrequently update it as Miui updates itself every week (https://github.com/MiCode https://github.com/MiCode). They don't have to really give any of that out since it's all Apache Licensed. However the ironic part is the areas of the Android source they must disclose under GPL, they avoid sharing. They don't release the kernel for any of their devices as well and that's a huge GPL violation. I would presume if they did release it for their own phones, it would be on here with the rest of their stuff. The rest of their official sites (there's a lot of non-affiliated English and other language sites that label themselves as Miui) are in Mandarin and much harder to navigate if you're an English speaker. Doing a google search for Xiaomi MI2 kernel source, turns up nothing positive about their kernel or about them and GPL though.