staging: vchiq: add more tasks to the TODO list

A short top-down description of this driver's architecture (function of

kthreads, userspace, limitations) could be very helpful for reviewers.

7) Review and comment memory barriers

There is a heavy use of memory barriers in this driver, it would be very

beneficial to go over all of them and, if correct, comment on their merits.

Extra points to whomever confidently reviews the remote_event_*() family of

functions.

8) Get rid of custom function return values

Most functions use a custom set of return values, we should force proper Linux

error numbers. Special care is needed for VCHIQ_RETRY.

9) Reformat core code with more sane indentations

The code follows the 80 characters limitation yet tends to go 3 or 4 levels of

indentation deep making it very unpleasant to read. This is specially relevant

in the character driver ioctl code and in the core thread functions.

10) Reorganize file structure: Move char driver to it's own file and join both

platform files

The cdev is defined alongside with the platform code in vchiq_arm.c. It would

be nice to completely decouple it from the actual core code. For instance to be

able to use bcm2835-audio without having /dev/vchiq created. One could argue

it's better for security reasons or general cleanliness. It could even be

interesting to create two different kernel modules, something the likes of

vchiq-core.ko and vchiq-dev.ko. This would also ease the upstreaming process.

The code in vchiq_bcm2835_arm.c should fit in the generic platform file.

12) Get rid of all the struct typedefs

Most structs are typedefd, it's not encouraged in the kernel.

13) Get rid of all non essential global structures and create a proper per

device structure

The first thing one generally sees in a probe function is a memory allocation

for all the device specific data. This structure is then passed all over the

driver. This is good practice since it makes the driver work regardless of the

number of devices probed.