Hello, Dick!
Thanks for your help so far!
linux-os (Dick Johnson) wrote:
You are trying to do it backwards. You need to have your driver
use get_dma_pages() to acquire pages suitable for DMA. Your
driver then impliments mmap().
Okay, I have seen that, too. I've seen that some drivers do it the other
way around as I do, but I still try to follow my idea that the
application allocs the memory and the dma / the driver fills it up.
Or are there fundamental problems I get with my approach which I haven't seen yet?
The user-mode application then mmaps() the dma-able pages into
its address-space. FYI, the pages may be from anywhere, some
archs can only DMA to/from memory below 16MB.
My DMA machine (ppc32, mpc8540 cpu) can do the whole 32bit phys address
space so, that's not an issue here.
The pages do not have
to be continuous because you will build a scatter-list for
the DMA engine and you will mmap() the pages so they are
contiguous to the user.
Yes, only virtual space is contigous. The DMA can do nice
sg_lists and chained sg_lists, so, this should not be a problem,
too.
Also 400 Megabytes is absurd.
Why?
Actually I am planning to alloc more than 1.5GByte at once,
lock that down, build a big sg_list for all that memory because
I need to _continously_ feed it with data from the DMA. I get
about 200MBytes/sec and I cannot stop in between!
Greets,
Clemens
On Thu, 4 Aug 2005, Clemens Koller wrote:
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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Cheers,
Dick Johnson
Penguin : Linux version 2.6.12 on an i686 machine (5537.79 BogoMips).
Warning : 98.36% of all statistics are fiction.
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I apologize for the following. I tried to kill it with the above dot :
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