[PATCH] drm/gem: Warn on illegal use of the dumb buffer interface v2

[Chris Wilson]

On Fri, Nov 21, 2014 at 03:48:33PM +0100, Thomas Hellstrom wrote:
> On 11/21/2014 03:14 PM, Chris Wilson wrote:
> > On Thu, Nov 20, 2014 at 09:56:25AM +0100, Thomas Hellstrom wrote:
> >> It happens on occasion that developers of generic user-space applications
> >> abuse the dumb buffer API to get hold of drm buffers that they can both
> >> mmap() and use for GPU acceleration, using the assumptions that dumb buffers
> >> and buffers available for GPU are
> >> a) The same type and can be aribtrarily type-casted.
> >> b) fully coherent.
> > Both (a) and (b) are true for intel and it turns out to be a requirement
> > for smooth transitions from the boot splash screens into X, and relied
> > upon by userspace.
> > -Chris
> >
> 
> So when you say relied upon by user-space, do you mean generic
> user-space or driver-specific user-space?
> 
> With that, I mean what component is responsible for deciding that the
> dumb buffer can be accelerated? The Intel xorg driver?

There is no way for the driver to know it has a dumb buffer. It copies
the contents of the current framebuffer onto its replacement framebuffer
so that it can do a seamless switch.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre