Hi Steven, On Mon, 5 Jul 2021 09:22:39 +0100 Steven Price <steven.price@xxxxxxx> wrote: > On 02/07/2021 19:11, Boris Brezillon wrote: > > On Fri, 2 Jul 2021 12:49:55 -0400 > > Alyssa Rosenzweig <alyssa@xxxxxxxxxxxxx> wrote: > > > >>>> ``` > >>>>> #define PANFROST_BO_REF_EXCLUSIVE 0x1 > >>>>> +#define PANFROST_BO_REF_NO_IMPLICIT_DEP 0x2 > >>>> ``` > >>>> > >>>> This seems logically backwards. NO_IMPLICIT_DEP makes sense if we're > >>>> trying to keep backwards compatibility, but here you're crafting a new > >>>> interface totally from scratch. If anything, isn't BO_REF_IMPLICIT_DEP > >>>> the flag you'd want? > >>> > >>> AFAICT, all other drivers make the no-implicit-dep an opt-in, and I > >>> didn't want to do things differently in panfrost. But if that's really > >>> an issue, I can make it an opt-out. > >> > >> I don't have strong feelings either way. I was just under the > >> impressions other drivers did this for b/w compat reasons which don't > >> apply here. > > > > Okay, I think I'll keep it like that unless there's a strong reason to > > make no-implicit dep the default. It's safer to oversync than the skip > > the synchronization, so it does feel like something the user should > > explicitly enable. > > I don't have strong feelings - ultimately the number of projects caring > about the uABI is so limited the "default" is pretty irrelevant (it's > not as if we are needing to guide random developers who are new to the > interface). But a conservative default seems sensible. > > >> > >>>> Hmm. I'm not /opposed/ and I know kbase uses strides but it seems like > >>>> somewhat unwarranted complexity, and there is a combinatoric explosion > >>>> here (if jobs, bo refs, and syncobj refs use 3 different versions, as > >>>> this encoding permits... as opposed to just specifying a UABI version or > >>>> something like that) > >>> > >>> Sounds like a good idea. I'll add a version field and map that > >>> to a <job_stride,bo_ref_stride,syncobj_ref_stride> tuple. > >> > >> Cc Steven, does this make sense? > > > > I have this approach working, and I must admit I prefer it to the > > per-object stride field passed to the submit struct. > > > > There are benefits both ways: > > * Version number: easier to think about, and less worries about > combinatorial explosion of possible options to test. > > * Explicit structure sizes/strides: much harder to accidentally forgot > to change, clients 'naturally' move to newer versions just with recompiling. The version I just sent has a PANFROST_SUBMIT_BATCH_VERSION macro defined in the the uAPI header, so getting right without changing the code should be fine (same has with the sizeof(struct xx)) trick with the per-desc stride approach). > > For now I'd be tempted to go for the version number, but I suspect we > should also ensure there's a generic 'flags' field in there. That would > allow us to introduce new features/behaviours in a way which can be > backported more easily if necessary. Adding features at the submit level without changing the version number is already possible (we can extend drm_panfrost_batch_submit without breaking the uABI), but I'm not sure that's a good idea... If you mean adding a flags field at the job level, I can add it, but I wonder what you have in mind when you say some features might be interesting to backport. I really thought we'd force people to update their kernel when they want those new features. Regards, Boris
