From: Jon M. Taylor <taylorj@gaia.ecs.csus.edu>
  To  : ggi-develop@eskimo.com
  Date: Wed, 12 May 1999 13:03:47 -0700 (PDT)

Re: MMIO accel with kgicon drivers.

On Tue, 11 May 1999, Marcus Sundberg wrote:

> Jon M. Taylor wrote:
> > 
> > On Tue, 11 May 1999, Marcus Sundberg wrote:
> > > > What is really needed for a
> > > > good solution to this problem is accel-operation FIFOs to reduce the
> > > > number of kernel-user transitions, as this is what kills performance.
> > > > Steffen's new KGI 0.9 design has exactly this, for exactly this reason.
> > >
> > > The old Dali KGI had it too, but unfortunately there was only one
> > > driver that used it... (the Mystique)
> > 
> >         Are you talking about the 'pingpong buffers'?
> 
> Yes. Well FIFO might not be the right thing to call it.

	If the buffer is always drained linearly, sure it does.  It just has
a fixed block size instead of being per-longword or per-accelblock. 

> > > For KGI 0.9 it probably will require root privs
> > > (or my preference - a separate device which you can give whatever
> > > permissions you want)
> > 
> >         I would do any such non-framebuffer mappings through device-specific
> > /proc entries created on the fly.  I am considering using such a scheme for
> > my Creative driver - accel buffers, texture buffers, vertex buffers, MMIO
> > registers (when appropriate) etc can all be handled this way and it keeps the
> > fbdev interface clean of driver-specific stuff. Perhaps ioctls could be
> > bound to each /proc file as well so that /dev/fb does not have to handle them
> > all.  This use of multiple ioctl entrypoints could provide a speed boost, but
> > I do not know if /proc entries are normal device files which handle
> > ioctls....
> 
> Proc entries can have a struct file_operations associated with them,
> so they can basicly do everyting a device node can do.
> But another (and IMHO more suitable) alternative is the devfs
> filesystem which will hopefully go into early 2.3 kernels.
> I've been using devfs for the last months and it's really nice.

	What is the effective functional difference between dynamically-created 
/proc entries and devfs entries?  Other than devfs is supposed to be 
backwards-compatible with existing /dev-using code....

Jon

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