On Mon, Jun 22, 2015 at 12:59:00PM +0100, Dave Gordon wrote: > On 19/06/15 09:44, Chris Wilson wrote: > > On Thu, Jun 18, 2015 at 07:07:46PM +0100, Dave Gordon wrote: > >> On 18/06/15 13:10, Chris Wilson wrote: > >>> On Thu, Jun 18, 2015 at 12:49:55PM +0100, Dave Gordon wrote: > >>>> On 17/06/15 13:02, Daniel Vetter wrote: > >>>>> Domain handling is required for all gem objects, and the resulting bugs if > >>>>> you don't for one-off objects are absolutely no fun to track down. > >>>> > >>>> Is it not the case that the new object returned by > >>>> i915_gem_alloc_object() is > >>>> (a) of a type that can be mapped into the GTT, and > >>>> (b) initially in the CPU domain for both reading and writing? > >>>> > >>>> So AFAICS the allocate-and-fill function I'm describing (to appear in > >>>> next patch series respin) doesn't need any further domain handling. > >>> > >>> A i915_gem_object_create_from_data() is a reasonable addition, and I > >>> suspect it will make the code a bit more succinct. > >> > >> I shall adopt this name for it :) > >> > >>> Whilst your statement is true today, calling set_domain is then a no-op, > >>> and helps document how you use the object and so reduces the likelihood > >>> of us introducing bugs in the future. > >>> -Chris > >> > >> So here's the new function ... where should the set-to-cpu-domain go? > >> After the pin_pages and before the sg_copy_from_buffer? > > > > Either, since the domain will not change whilst you have the lock, > > but if you do it before get_pages() you will have a slightly easier > > error path. > > OK, call to i915_gem_object_set_to_cpu_domain(obj, true) added right > after the i915_gem_alloc_object(); also, since we now have multiple > failure paths where the ability to distinguish them might be useful (and > since this function is a public addition to the gem_object repertoire), > I've made it return object-or-error-code, with the incomplete-copy case > returning ERR_PTR(-EIO). I'd stick to only using EIO when we have a GPU failure. Incomplete copy is EFAULT. > > Part of the reason why I want a function like this is so that I can > > replace it with a stolen object and so need to write the data through a > > temporary GGTT mapping. Speak now if you need more flags to the function > > to prevent certain classes of objects being created. > > -Chris > > For the GuC, the firmware image is written once by the CPU and > thereafter read only by the DMA engine via a GGTT address; other uC > devices might have different requirements e.g. the CSR/DMC doesn't have > a DMA engine AFAIK and the f/w is transferred to the h/w via MMIO writes > by the CPU. The primary reason for storing the image in a GEM object > (rather than kmalloc'd space, as the DMC loader does) is to make it > pageable; it's needed multiple times, as we have to reload the f/w after > reset or on exit from low-power states, but not used the rest of the > time. So the existing objects seem a good match. > > The GuC's pool and log objects, OTOH, must be permanently resident in > RAM and permanently mapped via the GGTT above GUC_WOPCM_OFFSET. So for > these it would be useful to have an allocator that *didn't* make the > object shmfs-backed. http://cgit.freedesktop.org/~ickle/linux-2.6/commit/?h=nightly&id=3f74a251aa9a3e5c1215226f7857ed53693c563f Though I want to use stolen as much as is practically possible, however without direct CPU access, stolen is very much an idle fancy. -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
