Empty IN_FORMATS in sun4i-drm

[Simon Ser]

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