On Wed, Feb 11, 2015 at 7:56 AM, Daniel Vetter <daniel@xxxxxxxx> wrote: > On Wed, Feb 11, 2015 at 06:23:52AM -0500, Rob Clark wrote: >> On Wed, Feb 11, 2015 at 6:12 AM, Russell King - ARM Linux >> <linux@xxxxxxxxxxxxxxxx> wrote: >> > As I've already pointed out, there's a major problem if you have already >> > had a less restrictive attachment which has an active mapping, and a new >> > more restrictive attachment comes along later. >> > >> > It seems from Rob's descriptions that we also need another flag in the >> > importer to indicate whether it wants to have a valid struct page in the >> > scatter list, or whether it (correctly) uses the DMA accessors on the >> > scatter list - so that exporters can reject importers which are buggy. >> >> to be completely generic, we would really need a way that the device >> could take over only just the last iommu (in case there were multiple >> levels of address translation).. > > I still hold that if the dma api steals the iommu your gpu needs for > context switching then that's a bug in the platform setup code. dma api > really doesn't have any concept of switchable hw contexts. So trying to > work around this brokeness by mandating it as a valid dma-buf use-case is > totally backwards. sure, my only point is that if I'm the odd man out, I can live with a hack (ie. requiring drm/msm to be aware enough of the platform to know if there is >1 level of address translation and frob'ing my 'struct device' accordingly)... no point in a generic solution for one user. I like to be practical. BR, -R > -Daniel > -- > Daniel Vetter > Software Engineer, Intel Corporation > +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>