On Fri, Apr 8, 2016 at 1:18 PM, Alan Corey wrote: > I haven't looked into it far enough, but why can't Linux use Android's > device drivers that already exist? Do the hardware manufacturers own > them? It doesn't seem like it should be that different from a video > card or a network card driver. Google claims most of Android is open > source. The pace may be a bit much, phones come on the market and > become obsolete much quicker than other hardware. As I type into my > 14 year old desktop...
It is complicated... A big part of it is the differences between ARM and PC architectures. Also, for years there was the Android fork of the Linux kernel, which had a bunch of new APIs but is mostly or all merged into mainline Linux these days I think(?). The vendors of CPUs, SoCs and mobile devices then forked from the Android fork of Linux, usually one fork per CPU, then one fork per SoC and one fork per mobile device, but sometimes some of those were shared within a vendor and some vendors did forward changes upstream. The Android-fork-specific APIs prevented sending drivers upstream to Linux mainline. In addition, the ARM architecture has no standard way of enumerating available devices and in Linux each device was supported by a compiled .c file and each Linux kernel binary could only run on one device. Linus got annoyed with this mess of .c files which leading to Linux on ARM adopting device-tree as a standard way to describe hardware. Right now, most devices don't ship device-tree files in the boot firmware but the Linux source tree has a repository of device-tree. This is changing as device-tree for ARM solidifies and becomes an ABI. In addition, each device vendor had their own boot mechanisms. More recently UEFI/ACPI have emerged as the standard boot mechanism for ARM servers so we may see that on mobile too at some point. At the same time, mobile devices have a life span of a couple of years due to the way people get them on phone network contracts. There often isn't enough time within two years to upstream all the changes into Linux mainline and once a device is out, there is no motivation to do that. The Linux kernel community meanwhile is using mobile devices but they work fine and they don't want to brick their phone, so they have no interest in mainlining that stuff. There is probably more to it than that, but this is the problem in a nutshell. Some links around this: https://lwn.net/SubscriberLink/682459/7e095da9f8e8fb2a/ https://lwn.net/Articles/616859/ https://lwn.net/Articles/573409/ https://lwn.net/Articles/572692/ http://elinux.org/CE_Workgroup_Device_Mainlining_Project https://lwn.net/Articles/662147/ https://lwn.net/Articles/481661/ https://lwn.net/Articles/472984/ https://lwn.net/Articles/514901/ https://lwn.net/Articles/647524/ http://elinux.org/LWN_Obstacles_article_details http://elinux.org/Kernel_Mainlining http://elinux.org/Mainlining_improvement_ideas -- bye, pabs https://wiki.debian.org/PaulWise
