On Mon, 2011-05-30 at 01:12 +0200, Tormod Volden wrote:
From: Tormod Volden debian.tormod@gmail.com
Drivers using multiple framebuffers got broken by commit 41c2e75e60200a860a74b7c84a6375c105e7437f which ignored the framebuffer (or register) map offset when looking for existing maps. The rationale was that the kernel-userspace ABI is fixed at a 32-bit offset, so the real offsets could not always be handed over for comparison.
Instead of ignoring the offset we will compare the lower 32 bit. Drivers using multiple framebuffers should just make sure that the lower 32 bit are different. The existing drivers in question are practically limited to 32-bit systems so that should be fine for them.
It is assumed that current drivers always specify a correct framebuffer map offset, even if this offset was ignored since above commit. So this patch should not change anything for drivers using only one framebuffer.
Drivers needing multiple framebuffers with 64-bit map offsets will need to cook up something, for instance keeping an ID in the lower bits, which is to be aligned away when it comes to using the offset.
Signed-off-by: Tormod Volden debian.tormod@gmail.com
What about this idea? (Untested patch)
If you test it and it works I like it best. Simple and clear, and pretty close to what I was thinking was a good idea.
As you say if someone needs this functionality in a new driver they can fix it, but really new drivers shouldn't be doing anything in this area.
Dave.