Messages in this thread | | | Date | Tue, 15 Dec 2009 16:20:56 -0800 | From | Earl Chew <> | Subject | Re: [PATCH 1/1] Userspace I/O (UIO): Add support for userspace DMA |
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Hans J. Koch wrote: > One example: An A/D converter has an on-chip 32k buffer. It causes an > interrupt as soon as the buffer is filled up to a certain high-water mark. > Such cases would easily fit into the current UIO system. The UIO core could > simply DMA the data to one of the mappings. A new flag for that mapping and > a few other changes are all it takes. After the DMA transfer is complete, the > interrupt is passed on to userspace, which would find the buffer already > filled with the desired data. Just a thought, unfortunately I haven't got > such hardware to try it.
Hans,
Is this case already covered by the pre-existing UIO_MEM_LOGICAL option ?
I'm thinking that since the memory is statically defined, it can be described using one of the existing struct uio_mem mem[] slots in struct uio_info and marked as UIO_MEM_LOGICAL.
The userspace program can map that into its process space using the existing mmap() interface.
What am I missing?
> When it comes to dynamically allocated DMA buffers, it might well be possible > to add a new directory in sysfs besides the "mem" directory, e.g. something > like /sys/class/uio/uioN/dma-mem/. This would save us the trouble of creating > a new device. Maybe the example above would better fit in here, too. Who knows.
I looked at the 2.6.32 source at
http://lxr.linux.no/#linux+v2.6.32/drivers/uio/uio.c
and didn't see any reference to /sys/class/uio/uioN/mem . Perhaps you're referring to something new.
In any case, I think you're describing adding
/sys/class/uio/uioN/dma-mem
as a means to control /dev/uioN . Presumably writing to /sys/class/uio/uioN/dma-mem would create additional dynamic DMA buffers.
I can't yet see a way to make this request-response. When requesting a dynamic buffer I need to indicate the size that I want, and in return I need to obtain a handle to the buffer (either its mapping number, address, etc). Once I have that, I can query other interesting information (eg its bus address).
Earl
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