How to test whether a buffer is in linear format

[Simon Ser]

On Saturday, August 6th, 2022 at 21:56, Hoosier, Matt <Matt.Hoosier at garmin.com> wrote:

> Any idea what’s up with some compositors adding code to infer
> DRM_FORMAT_MOD_LINEAR semantics when the buffer’s modifiers are set
> to 0?

What does that mean? A buffer only has a single modifier, and LINEAR == 0.

> Wlroots, for example, added this as a “safety net for drm drivers not announcing modifiers”.
> 
> https://source.puri.sm/Librem5/wlroots/-/merge_requests/63

This is not upstream wlroots. This change doesn't make sense to me at
all. Either a driver supports modifiers and advertises support for it,
either it doesn't and gbm_surface_create_with_modifiers fails. At any
rate, forcing LINEAR in this code-path doesn't make sense.