Is it possible to separate amba-pl011 device driver from linux kernel and move the driver to run on a separate standalone system/processor?
How should I do that in a clean way?

This code is very Linux-specific. Moving it out is possible, but requires nearly the same time than writing the thing from scratch in user space.

Basically: "you can't. Don't try."

Thanks, Mara.
May I know why you say it takes the same time to writing from scratch in user space. Is that the 2nd option I can try out?

Do you have any idea how to move the driver out from kernel? I found the code are referencing each other heavily and I don't know from where I should start with it.
Can you please give me some idea by using amba-pl011 as an example?

Thanks a lot.

Sundialsvcs, may I know why you say so?

First, take all functions that use writew() and readw(). They talk to the hardware. If you're moving the code to userspace, you need something that will allow you to read/write to device memory space. You can make a small driver for that. Then change all the calls to writew/readw to the right calls to that driver. Already that will take much time. Then you need to remove all the other things that do not compile: write your own handling of scatter-gather buffers (sg_* functions), handle interrupts, start and stop the device.

I really do not understand why you want it in userspace. Could you explain?

Thanks a lot, Mara.
Actually I don't plan to move it to user space, but it could be an option for me if my initial idea cannot work out.

I am thinking to move a certain driver, such as uart(amba-pl011) to run on another cpu, separated from the cpu that runs the Linux kernel.
Currently we have the monolithic kernel running on a cpu. I would like to dedicate another cpu to take care of a certain device, but the kernel that runs on the separated cpu is still the master to that device (driver). In order to achieve this, I need to take out the uart driver from kernel and make it a standalone code running on the second cpu. There will be some communication methods applied to the inter-cpu and user still sees the uart device under the Linux system.
I have no idea how should I separate the uart driver to make it an independent code, while still preserve its compatible with Linux kernel.

Thanks for explanation. When you move the driver to other OS (have you looked into the licensing issues?), it will stop beeing compatible with Linux. You'll have to use another interrupt, DMA and memory management subsystems. It may be functionally fine, however, if you have all the functions you need in that other OS.