On Tue, 27 Jul 2021 23:08:40 -0700, Petri Latvala wrote: > > On Tue, Jul 27, 2021 at 07:01:24PM -0700, Dixit, Ashutosh wrote: > > On Mon, 26 Jul 2021 05:03:04 -0700, Matthew Auld wrote: > > > > > > diff --git a/lib/i915/gem_mman.c b/lib/i915/gem_mman.c > > > index 4b4f2114..e2514f0c 100644 > > > --- a/lib/i915/gem_mman.c > > > +++ b/lib/i915/gem_mman.c > > > @@ -497,6 +497,43 @@ void *gem_mmap_offset__cpu(int fd, uint32_t handle, uint64_t offset, > > > return ptr; > > > } > > > > > > +#define LOCAL_I915_MMAP_OFFSET_FIXED 4 > > > > Cc: @Petri Latvala > > > > This use of LOCAL declarations is more related to the methodology we follow > > in IGT rather than this patch. We have seen in the past that such LOCAL's > > linger on in the code for months and years till someone decides to clean > > them so the question is can we prevent these LOCAL's from getting > > introduced in the first place. > > > > One reason for these is that we sync IGT headers with drm-next whereas IGT > > is used to test drm-tip. So the delta between the two results in such > > LOCAL's as in this case. > > > > My proposal is that even if we don't start sync'ing IGT headers with > > drm-tip (instead of drm-next) we allow direct modification of the headers > > when needed to avoid introducing such LOCAL's. So in the above case we > > would add: > > > > #define I915_MMAP_OFFSET_FIXED 4 > > > > to i915_drm.h as part of this patch and then just use > > I915_MMAP_OFFSET_FIXED. If another sync happens from drm-next before this > > #define has appeared there, the compile will break and whoever syncs will > > need to add this again to i915_drm.h. > > I don't like that kind of a breakage at all. That enforces mandatory > fixups to some poor developer working on unrelated code who doesn't > necessarily know how to even fix it easily. > > Of course an argument can be made that it's an i915 token in an i915 > header so it will be the i915 people doing it, but for a general case > that's going to cause more harm than it solves problems, I feel. OK, let's not change anything with the headers we import for now. > > What do people think about a scheme such as this? The other, perhaps > > better, option of course is to sync the headers directly with drm-tip > > (whenever and as often as needed). But the goal in both cases is to avoid > > LOCAL's, or other things like #ifndef's distributed throughout multiple > > source files which we also do in such cases. A centralized internal header > > to contain such declarations might not be so bad. Thanks. > > A separate manually written header for new tokens that are not yet in > drm-next might be the least bad of all options. Although now that I've > said it, the perfect world would have new tokens done like this: > > #ifndef I915_MMAP_OFFSET_FIXED > #define I915_MMAP_OFFSET_FIXED 4 > #else > _Static_assert(I915_MMAP_OFFSET_FIXED == 4, "ABI broken, yikes"); > #endif > > In a different language wrapping all that in a > > MAYBE_DECLARE(I915_MMAP_OFFSET_FIXED, 4) > > might be easier but with C preprocessor it's a bit more... involved. A > separate build-time script to generate that header maybe? Such a > script could also just completely omit the definition if header copies > already introduce the token. IMO all this wouldn't do much more that what gcc already does. For example, for this: #define I915_MMAP_OFFSET_FIXED 4 #define I915_MMAP_OFFSET_FIXED 4 gcc silently ignores the second #define, whereas for: #define I915_MMAP_OFFSET_FIXED 4 #define I915_MMAP_OFFSET_FIXED 5 gcc will warn that second I915_MMAP_OFFSET_FIXED is redefined. And gcc will error out on things like struct redeclaration. > Recap: > > 1) We have kernel headers copied into IGT to ensure it builds fine > without latest-and-greatest headers installed on the system. > > 2) Copies are from drm-next to ensure the next person to copy the > headers doesn't accidentally drop definitions that originate from a > vendor-specific tree. (That same reason is also for why one shouldn't > edit the headers manually) > > 3) To get to drm-next, the kernel code needs to be tested with IGT > first, so we need new definitions to test that kernel code in some > form. I guess it is possible to test with "Test-with:" and merge the kernel changes first and the IGT changes later with the correct headers but maybe it's inconvenient? But don't we merge the kernel changes before IGT? > 4) LOCAL_* definitions that are cleaned up later when actual > definitions reach drm-next sounds good in theory but in practice the > cleaning part is often forgotten. > > Either way, I think the code using new definitions should use the > intended final names so we should just entirely drop the practice of > declaring anything LOCAL_*. That way the cleanup is limited to one > place. In any case, any thoughts about the i915_drm_local.h patch I posted: https://patchwork.freedesktop.org/series/93096/ I am not asking for any other changes to anything at this this point. I have also started asking people to not use the LOCAL_ or local_ prefix any more in code reviews. But I probably still prefer that these declarations move to a central place such as i915_drm_local.h if possible so it's easier to clean them up later. Thanks. _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
