[PATCH v2 hwc] drm_hwcomposer: provide a common gralloc handle definition

[Rob Herring]

On Tue, Oct 31, 2017 at 11:44 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Tue, Oct 31, 2017 at 09:59:20AM -0500, Rob Herring wrote:
>> EGL, gralloc, and HWC must all have a common definition of fd's and int's
>> in native_handle_t to share the fd and width, height, format, etc. of a
>> dmabuf.

[...]

>> +#define GRALLOC_HANDLE_MAGIC 0x5f47424d
>
> Maybe add a
>
> #define GRALLOC_HANDLE_VERSION 1
> #define GRALLOC_HANDLE_MAGIC (0x5f47424d + GRALLOC_HANDLE_VERSION)
>
> and a comment that the version needs to be incremented for every change,
> to catch mismatching mesa/hwc versions? Given the layout there's no way to
> add more fds in a backwards-compatible way, so we need full versioning I
> think, and treat any change as a breaking one.

If we add or remove anything that will already be caught because sizes
are stored and checked.

The magic corresponds to 'GBM_'. Maybe we want to change that to
something else. However, I'd like to not change it just yet. My
intention was to keep it compatible, update gbm_gralloc and mesa
dependencies, then make any changes to this struct.

Rob