Re: User mode drivers: part 1, interrupt handling (patch for 2.6.11)

On Sat, 2005-03-12 at 21:03 -0500, Jon Smirl wrote:
> On Fri, 11 Mar 2005 19:14:13 +0000, Alan Cox <alan@lxorguk.ukuu.org.uk>
wrote:
> > I posted a proposal for this sometime ago because X has some uses for
> > it. The idea being you'd pass a struct that describes
> > 
> > 1.      What tells you an IRQ occurred on this device
> > 2.      How to clear it
> > 3.      How to enable/disable it.
> > 
> > Something like
> > 
> >         struct {
> >                 u8 type;                /* 8, 16, 32  I/O or MMIO */
> >                 u8 bar;                 /* PCI bar to use */
> >                 u32 offset;             /* Into bar */
> >                 u32 mask;               /* Bits to touch/compare */
> >                 u32 value;              /* Value to check against/set */
> >         }
> >
> 
> It might useful to add this to the main kernel API, and then over time
> modify all of the drivers to use it. If a driver does this it would be
> safe to transparently move it to user space like in UML or xen.  I've
> been told that PCI Express and MSI does not have this problem.
> 

This seems sufficient for the simplest devices, that just have an
IRQ_PENDING and an IRQ_ACK register.  But what about a device like the
emu10k1 where you have a half loop and loop interrupt for each of 64
channels, plus about 10 other interrupt sources?  The IPR just tells you
there's a channel loop interrupt pending, in order to properly ACK it
you need to set a bit in one of 4 registers depending on whether it's a
loop or half loop interrupt, and whether the channel is 0-31 or 32-64.

Lee