Re: How to get the physical page addresses from a kernel virtual address for DMA SG List?

["linux-os \(Dick Johnson\)" <linux-os@analogic.com>]

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().

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. 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. Also 400 Megabytes is absurd.

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 I've spent already a lot of time reading outdated things.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
> _______________________________
> R&D Imaging Devices
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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.
.
I apologize for the following. I tried to kill it with the above dot :

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