Hello!
This might be an FAQ - I've got several ideas from googling
around for days and reading 'Linux Device Drivers' or
'Understanding The Linux Kernel' which are both really good
books. However I am not really sure of how to do it on the latest
linux-2.6.
I am currently working on a dma driver for a ppc32 system.
The idea is that a userspace app allocates a big contigous
chunk of memory (i.e. 400MBytes, user virtual mem) and tells
my dma's char driver via ioctl the pointer to that memory.
In the driver I can now use that (void __user *) casted address
as a kernel virtual address, right? It's contigous there and I can
do a memcpy() to get data to userspace simliar to a copy_to_user().
fine!
But I want to setup a scatter/gather DMA list and blow my data
directly into the applications physical pages.
What's the best way to setup the dma_sg_list?
I have checked several things to get the pages and physical addresses
but with no real success now:
get_user_page()
vmalloc_to_page()
kvirt_to_bus() (deprecated?)
virt_to_phys()
virt_to_bus()
Or do I need to remap the whole thing before I can get all the pages and
physical addresses?
remap_page_range()
remap_pfn_range()
map_user_kiobuf()
unmap_kiobuf()
Or do I need the direct-io stuff or the block-io?
How do I need to alloc the mem in my app? (get_pages()?)
How do I need to lock the memory to make sure it's in phys memory? (mlockall()?)
Can somebody please put some light on what's _the_ way to do that on the
latest 2.6 kernels? I am pretty much confused which functions are current
and okay to use to solve my problem.
Pointers to some code is also very welcome. But it should be _current_.
I've spent already a lot of time reading outdated things. :-(
Best regards,
Clemens Koller
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