Re: mm->mmap_sem

["Benjamin C.R. LaHaise" <blah@kvack.org>]

On Wed, 29 Sep 1999, James Simmons wrote:

> On Thu, 30 Sep 1999, Stephen C. Tweedie wrote:
> 
> > Hi,
> > 
> > On Mon, 27 Sep 1999 15:31:28 -0400 (EDT), James Simmons
> > <jsimmons@edgeglobal.com> said:
> > 
> > > What are all the broken cards out their? I was reading my old Matrox
> > > Millenium I docs and even that card supports similutaneous access to 
> > > the accel engine and framebuffer. If the number of cards that are that
> > > broken are small then I just will not support them.
> > 
> > I think that there's a large number of them.  The XI and XFree86 folk
> > would probably know which ones exactly.
> 
> Yikes. I think the best solution is to just put the process that owns
> the framebuffer to be put to sleep just before accel engine access. Wake
> it up once its done. Some fancy scheduling tricks should do it. I have it
> setup now that accels used internal in the kernel to speed up console
> rendering will not work when /dev/fb is mmapped. Also I have set it up so
> only one process can open /dev/fb at a time. This makes life much easier.

No, same problem.  You can't put a process to sleep without
inter-processor interrupts on smp if its not running currently.  You can't
allow the kernel to touch the frame buffer if the user is using the
accelerator or vice-versa.  Have an ioctl to lock the kernel out from
updating, and only unlock it from user space when there's no activity for
a while.

		-ben

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