Did PCI/IRQ allocation change significantly after 4.2 kernel?

[Greg KH]

On Tue, Mar 29, 2016 at 04:11:22PM -0400, Rob Groner wrote:
> Your first glance is probably correct.  The driver handles reads and
> writes to registers via IOCTLs from the user library, as well as
> interrupts and DMA.  There are probably two main reasons the driver is
> structured like that: 1) All "new" drivers here are essentially tailored
> versions of previous drivers that have been around for a while, so this
> wasn't built-from-scratch new.  While it means that any poor design
> decisions made early on are perpetuated, it also means to us that we
> aren't re-inventing the wheel and we're mostly using a driver that has
> proven to work for quite a while.  2) The library code for the board is
> shared (internally) with our Windows driver package, and in some cases
> DOS too.  Since Windows uses IOCTLs, we can essentially share the exact
> same library files, and only the IOCTL call itself is OS-specific.
> 
> I know #1 is not a good reason and I'd be happy to work towards
> re-writing the driver in a more correct way, but probably not if it
> would cause us to have to split into a Linux and Windows library
> versions.  Keeping the library common at this point has saved us a lot
> of development time.

I understand the need for userspace libraries to be "unified", but you
might be able to get away with no kernel driver at all, just use the UIO
driver for your device and then read/write the memory mapped area of
your card directly from your library/application.  That will have the
benifit of making your Linux implementation faster as well :)

> I absolutely appreciate the feedback on driver design...I've never
> really received any and all I know about Linux drivers is what I read
> online, read in LDD, and what was in the drivers that existed when I
> came to work here.  Is the current form of the driver just "bad" or
> "intolerably bad"?

It's not "bad", but there is room for improvement to make it smaller and
more "flexible" (i.e. no static list of devices, use the pci driver
model better, etc.)  You should also make sure you are properly checking
your ioctl calls to ensure you don't have any security issues hiding
here, that wouldn't be good for your users.  I think you are doing this
correctly in dm35418_validate_pci_access(), but it would be good to
verify this again to be sure, your ioctl structures are a bit "odd" in
that they try to be generic so it's hard to really tell what you are
passing around.

thanks,

greg k-h