Re: UIO - interrupt performance

[Wolfgang Grandegger <wg@grandegger.com>]

Ben Nizette wrote:
> On Tue, 2008-10-21 at 11:30 +0200, Marco Stornelli wrote:
>> I could agree, but "the facto" due to UIO license condition, a company
>> often uses UIO drivers, regardless performance, debug, etc, only as not
>> to public the code under GPL.
> 
> It sounds to me like you think that driver authors can sit down and
> decide whether they want to implement their driver in userspace or
> kernel space.  For 99% of drivers that's simply not true.  You  *cannot*
> write userspace drivers for most hardware, the hooks just aren't
> available.  UIO is Userspace I/O, not a set of general hooks for
> userspace drivers.

I known, fortunately it's not that simple or even feasible. Image a
network driver with I/O multiplexing used by various processes.

> If people want drivers not under the GPL then they can distribute a
> binary-only module (though thank $DEITY there aren't many of those
> left).  Userspace I/O exists to provide good performance interfacing to

That's *not* an option, please read the GPL license conditions. At least
it's legal gray area. Note that it's not my intention to start a
discussion on that.

> a family of devices - those which exist just to shuffle data around and
> have an interrupt to tell you when they're done.
> 
> Do you have any example of a userspace i/o driver which exists to get
> around licencing constraints?

There will be plenty sooner than later. What you can do currently with
UIO is very limited.

Wolfgang.