On Thursday 22 May 2014 14:39:20 Nicolas Pitre wrote: > On Thu, 22 May 2014, Arnd Bergmann wrote: > > > On Thursday 22 May 2014 14:09:52 Nicolas Pitre wrote: > > > On Thu, 22 May 2014, Arnd Bergmann wrote: > > > > > > > On Thursday 22 May 2014 15:45:03 Catalin Marinas wrote: > > > > > By making the DMA memory Strongly Ordered, we avoid the > > > > > L220 write buffer. In addition to the above commit, we also had > > > > > 2503a5ecd86c (ARM: 6201/1: RealView: Do not use outer_sync() on > > > > > ARM11MPCore boards with L220). > > > > > > > > Ah, so this also stands in the way of multiplatform realview > > > > > > Isn't the real value of a multiplatform realview in the ability to use > > > it with Qemu? Did Qemu go to the extreme of emulating all those cache > > > issues? > > > > The qemu developers have in the past always argued strongly that they > > want to run the same kernel that runs on real hardware. Having a kernel > > that runs only on the emulated version but not on actual hardware is > > clearly against that goal, and we should use CONFIG_ARCH_VIRT for > > that purpose. > > But the kernel that actually runs on the real hardware also runs on Qemu > already. It is just that, by some coincidence, a multi-platform kernel > that pretends to have the same peripherals as a Realview board could > also be used on Qemu. > > Otherwise I really don't see the point in making the code more complex > just to make a multi-platform kernel run on actual Realview hardware > that is quite obsolete now and that very few people have access to. The main reason is that out of principle I want to get to the point where every ARMv6 and ARMv7 machine is part of CONFIG_ARCH_MULTIPLATFORM. Then again, once we introduce CONFIG_BROKEN_MULTIPLATFORM, we could have an option that depends on that, and turns on both ARM_DMA_MEM_BUFFERABLE as well as the hack to remove the outer_sync from mb() and wmb() for CONFIG_SMP. Arnd -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
