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SubjectRe: Userspace I/O driver core
Greg KH wrote:
> But in order to get this core into the kernel tree, we need to have some
> "real" drivers written that use it. So, for anyone that wants to see
> this go into the tree, now is the time to step forward and post your
> patches for hardware that this kind of driver interface is needed.
We have a product being developed currently for which this interface is

The situation is that we have Linux collecting data from very many
sources. The data is processed by throwing it at a memory address at
which an FPGA lives. The FPGA processes the data and generates an
interrupt upon completion at which time the processed data can be read
back out. Linux doesn't know anything about the data except it's source
and destination and, for security reasons, it has to stay that way. As
such a formal driver makes little sense: data gets written to a memory
address and a little while later it is read out again, that's it. The
only fly in the ointment is the interrupt. Before I knew about these
UIO patches I had written what effectively was a smaller version of UIO
to handle this interrupt. With the UIO patches the whole process
becomes trivial and I (along with my boss) become happy :-)

I shall submit a patch once I move my code over but it's almost not
worth it, it will be truly trivial.

I can see a similar scenario being played out a lot in industrial
control and other embedded systems. For example, if you just want to
monitor a set of data but interrupt if something critical happens (or
even just when the data is updated). All an in-kernel driver would do
is handle an interrupt and perform copy_{to,from}_user()s but it would
have to have a fair bit of fluff around it to signal to userland that
the interrupt had occured. UIO is a clean, standard and powerful form
of that fluff. Congrats to all who worked on her.

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