On Tue, Dec 13, 2011 at 07:10:02AM -0800, Arnd Bergmann wrote: > On Monday 12 December 2011, Robert Morell wrote: > > > > > > Doing a buffer sharing with something that is not GPL is not fun, as, if any > > > issue rises there, it would be impossible to discover if the problem is either > > > at the closed-source driver or at the open source one. At the time I was using > > > the Nvidia proprietary driver, it was very common to have unexplained issues > > > caused likely by bad code there at the buffer management code, causing X > > > applications and extensions (like xv) to break. > > > > > > We should really make this EXPORT_SYMBOL_GPL(), in order to be able to latter > > > debug future share buffer issues, when needed. > > > > Sorry, I don't buy this argument. Making these exports GPL-only is not > > likely to cause anybody to open-source their driver, but will rather > > just cause them to use yet more closed-source code that is even less > > debuggable than this would be, to those without access to the source. > > But at least the broken module then won't be interacting with other modules > because it cannot share any buffers. One of the goals of this project is to unify the fragmented space of the ARM SoC memory managers so that each vendor doesn't implement their own, and they can all be closer to mainline. I fear that restricting the use of this buffer sharing mechanism to GPL drivers only will prevent that goal from being achieved, if an SoC driver has to interact with modules that use a non-GPL license. As a hypothetical example, consider laptops that have multiple GPUs. Today, these ship with onboard graphics (integrated to the CPU or chipset) along with a discrete GPU, where in many cases only the onboard graphics can actually display to the screen. In order for anything rendered by the discrete GPU to be displayed, it has to be copied to memory available for the smaller onboard graphics to texture from or display directly. Obviously, that's best done by sharing dma buffers rather than bouncing them through the GPU. It's not much of a stretch to imagine that we'll see such systems with a Tegra CPU/GPU plus a discrete GPU in the future; in that case, we'd want to be able to share memory between the discrete GPU and the Tegra system. In that scenario, if this interface is GPL-only, we'd be unable to adopt the dma_buffer sharing mechanism for Tegra. (This isn't too pie-in-the-sky, either; people are already combining Tegra with discrete GPUs: http://blogs.nvidia.com/2011/11/world%e2%80%99s-first-arm-based-supercomputer-to-launch-in-barcelona/ ) Thanks, Robert -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>