Empty IN_FORMATS in sun4i-drm

[Emmanuel Gil Peyrot]

Hi,

After updating Weston from 9f8561e9 to 07326040 (latest master), it
fails to run on my PinePhone saying “format 0x34325258 not supported by
output DSI-1” and then exiting.

This format is XR24, which would be extremely surprising not to be
present, and drm_info[1] says it is present.  Looking into Weston’s
code, I found that drm_plane_populate_formats()’s docstring says it uses
“either the IN_FORMATS blob property (if available), or the plane's
format list if not.”  Looking back at drm_info, I saw said IN_FORMATS
blob being empty of formats (while the format list is fully populated):
"IN_FORMATS" (immutable): blob = 32
└───DRM_FORMAT_MOD_LINEAR (0x0)

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.

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

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

Thanks,

[1] https://github.com/ascent12/drm_info

-- 
Emmanuel Gil Peyrot
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