Help needed with device driver

[Dave Olson]

In <9102142334.AA03699 at igor.tamri.com> rickm at IGOR.TAMRI.COM (Rick marsh) writes:


| Some questions that relate to a device driver that I need to write. It
| will run initially on a Personal Iris.
| 
| 1. We need to translate virtual addresses to physical addresses, in order
| to do dma transfers. The only routine that appears to do this is kvtophys(),
| this translates kernel virtual addresses to physical addresses. Is there a
| routine that translates user virtual addresses to physical addresses ?

kvtophys is pretty much it, although there are some special cases.

| 2. If there is not, and we are forced to use kvtophys(), is there a routine
| that maps user virtual memory to kernel virtual memory ? It appears that
| physio() does this but we don't want to call physio() because it does
| several other things that we do not need (We don't want to do the dma transfer
| at the time that we do the virtual to physical translation).

If you don't do it at the time of the copy/io, then the physical address
could be different by the time you actually wanted to do the i/o, unless
you lock the pages down.

| 3. mpin() locks pages into physical memory, is it at all possible that a page,
| once locked, would be moved around in memory? We intend to do the dma transfer
| some time after doing the virtual to physical translation and moving pages
| would be a disaster.

As I recall, the answer is no, but what is your objection to doing the
address translation at the time of the DMA?  It isn't all that expensive to
do it, and locking down lots of memory can be pretty anti-social.

For more detailed answers to these questions, and device drivers in
general, get the following document:

SGI Document #007-0911-010
Writing Device Drivers for Silicon Graphics Computer Systems
--

	Dave Olson

Life would be so much easier if we could just look at the source code.