On Tuesday, December 14th, 2021 at 15:49, Emmanuel Gil Peyrot linkmauve@linkmauve.fr wrote:

This makes me think the kernel should populate IN_FORMATS with at least the same formats as the format list when supported, or stop advertising this property altogether.

Yup. This is a bug in the driver.

Other compositors (such as phoc) still run file, probably because they use the format list exclusively, without consideration for modifiers.

phoc is based on wlroots, which falls back to its modifier-less codepath when a driver is missing IN_FORMATS (or if it's empty). But it does support modifier-aware buffer allocation as well.

Besides fixing this driver, would it make sense to also make Weston ignore an empty IN_FORMATS and fall back to the format list?

I'd rather not, because this makes it more difficult to find buggy drivers.