On Wed, Jan 31, 2018 at 08:42:12AM +0100, Maxime Ripard wrote: > Hi Liviu, Hi Maxime, > > On Wed, Jan 31, 2018 at 03:08:08AM +0000, Liviu Dudau wrote: > > On Fri, Jan 26, 2018 at 11:00:41AM +0800, Yong wrote: > > > Hi Maxime, > > > > > > On Fri, 26 Jan 2018 09:46:58 +0800 > > > Yong <yong.deng@xxxxxxxxxxxx> wrote: > > > > > > > Hi Maxime, > > > > > > > > Do you have any experience in solving this problem? > > > > It seems the PHYS_OFFSET maybe undeclared when the ARCH is not arm. > > > > > > Got it. > > > Should I add 'depends on ARM' in Kconfig? > > > > No, I don't think you should do that, you should fix the code. > > > > The dma_addr_t addr that you've got is ideally coming from dma_alloc_coherent(), > > in which case the addr is already "suitable" for use by the device (because the > > bus where the device is attached to does all the address translations). > > Like we're discussing in that other part of the thread with Thierry > and Arnd, things are slightly more complicated than that :) Yeah, sorry, my threading of the discussion was broken and I've seen the rest of the thread after I have replied. My bad! > > In our case, the bus where the device is attached will not do the > address translations, and shouldn't. In my view, the bus is already doing address translation at physical level, AFAIU it remaps the memory to zero. What you (we?) need is a simple bus driver that registers the correct virt_to_bus()/bus_to_virt() hooks for the device that do this translation at the DMA API level as well. > > > If you apply PHYS_OFFSET forcefully to it you might get unexpected > > results. > > Out of curiosity, what would be these unexpected results? If in the future (or a parallel world setup) the device is sitting behind an IOMMU, the addr value might well be smaller than PHYS_OFFSET and you will under-wrap, possibly starting to hit kernel physical addresses (or anything sitting at the top of the physical memory). >From my time playing with IOMMUs and PCI domains, I've learned to treat the dma_addr_t as a cookie value and never try to do arithmetics with it. Best regards, Liviu > > Thanks! > Maxime > > -- > Maxime Ripard, Free Electrons > Embedded Linux and Kernel engineering > http://free-electrons.com > > -- > You received this message because you are subscribed to the Google Groups "linux-sunxi" group. > To unsubscribe from this group and stop receiving emails from it, send an email to linux-sunxi+unsubscribe@xxxxxxxxxxxxxxxx. > For more options, visit https://groups.google.com/d/optout.
