On 22/06/15 13:37, Chris Wilson wrote: > 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. Done, it now returns -EFAULT on incomplete copy. >>> 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 Yes, that looks useful ... .Dave. _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
