On Wed, Mar 29, 2017 at 10:51:05AM -0600, Shuah Khan wrote: > Hi Russell, > > On Wed, Mar 29, 2017 at 10:33 AM, Russell King - ARM Linux > <linux@xxxxxxxxxxxxxxx> wrote: > > Okay, I'm about to merge the following patch for -rc, since refusing > > to create a scattertable for non-page backed memory is the only valid > > solution for that case. I'm intending to queue this for -rc this > > evening. > > I was bit sidetracked and getting back to this today. I am just about > to test this change on my system. I will test your patch and send you > results. > > This might not help my use-case - I suspect it will trip this check. > That said I will send you results very soon. I do hope that it _does_ trip this check - the result should be that you get an error without the kernel oopsing. > I have been thinking about this some. I would like to see if we can > provide a way forward to address the cases where coherent memory is > not guaranteed to be backed by struct pages. We know the memory isn't > backed at alloc time in dma_alloc_coherent(). Can we key off of that > maybe add a new attr flag to avoid page lookups. I am willing to work > on the fixing it. What we need is to revise the dma-buf API and DMA APIs to allow passing coherent memory through it - there is no current provision in the DMA APIs to have coherent memory mapped for two peripherals. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.