[RFC PATCH] Documentation: devicetree: add description for generic bus properties

[Dave Martin]

On Fri, Nov 29, 2013 at 09:57:03AM +0000, Russell King - ARM Linux wrote:
> On Fri, Nov 29, 2013 at 10:37:14AM +0100, Thierry Reding wrote:
> > There's a large gap between how fast new SoCs are supposed to tape out
> > and the rate at which new code can be merged upstream. Perhaps some of
> > that could be mitigated by putting more of the complexity into firmware
> > and that's already happening to some degree for ARMv8. But I suspect
> > there's a limit to what you can hide away in firmware while at the same
> > time giving the kernel enough information to do the right thing.
> 
> One of the bigger issues which stands in the way of companies caring
> about mainstream support is closed source IPs like VPUs and GPUs.
> 
> If you have one of those on your chip, even if the kernel side code
> is already under the GPL, normally that code is not "mainline worthy".
> Also, as the userspace code may not be open source, some people object
> to having the open source part in the kernel.
> 
> So for customers to be able to get the performance out of the chip,
> they have to stick with having non-mainline kernel.
> 
> At that point, why bother spending too much time getting mainline
> support for the device.  It's never going to be fully functional in
> mainline.  It doesn't make sense for these SoC companies.

Putting effort into upstream support for something that is only relevant
to GPUs (or VPUs) does look less valuable for us right now, unless it
encourages people to start posting more GPU/VPU code upstream, and we
know there are other blockers there.

DMA and IOMMU we definitely care about, though.

Cheers
---Dave