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The Ugly State of ARM Support On Linux
jfruhlinger writes "Power-efficient ARM processors are moving up the food chain, to the extent that even Windows will soon see an ARM port. Linux, which has long been cross-platform, should have a long head start in this niche, right? Well, blogger Brian Proffitt explains just how messy the state of Linux support for ARM is right now, partially as a result of mutually conflicting kernel hacks from ARM manufacturers who just wanted to get their products out the door and weren't necessarily abiding by the GPL obligations to release code. Things are improving now, not least because Linus is taking a personal hand in things, but sorting the mess out will take time."
Having worked on bring-up on three custom ARM projects, I can personally attest to how gnarly it can be. But it's not necessarily something that Linus will be able to fix, or the Linux kernel community at large.
The main problem is the custom board support - even though the source code is GPL, they give you full source code and even submit it to back into the eco-system, it's just haphazard code that was pushed out the door too quickly. Linus can't stop people from writing bad kernel code, he can stop them from submitting it back into the mainline, but thats kind of what we have right now. If your code isn't up to snuff it doesn't make it into mainline. That doesn't stop them from shipping a product and giving that code to customers.
In one case, the documentation for the ARM chip I recieved was a password protected PDF that you can't even cut text out of, describing how to use the features by writing your own device driver. In that case, they had minimal Linux support but for all the bells and whistles you had to do it yourself.
The problem is as dense and layered as the chips themselves - what really needs to happen is a standardized method for publishing SoC features in a structured format (XML?) where common features (FIFO registers with a bytes_remaining field? Write only configuration registers, Read only configuration register.. etc) could be defined and the code could in many cases just be automatically generated.
Need to set reg A to all f's, reg B to all zeros, flip bit 12 of reg C and then your PHY is configured - done.
For more complex interlocking mechanisms that would be difficult or impossible to communicate in a cure-all DSL, but even if you could eliminate 80% of the problems that'd be great.
Which brings me to the other problem - a lot of what you do to get ARM systems up and running happens way before you run Linux - in U-Boot/RedBoot or whatever else is out there.. And thats a whole other kettle of fish.