Non-atomic kms drivers like radeon-kms (or nouveau-kms with
default setting of "atomic ioctl disabled") don't export
any formats, so num_formats == 0.
Some atomic drivers (nouveau-kms with boot param nouveau.atomic=1,
or intel-kms on, e.g., Linux 4.13) expose num_formats == 0, or
don't expose any modifiers, so num_modifiers == 0.
Let the drmmode_is_format_supported() check pass in these cases
to allow page flipping, as it works just fine.
Tested on NV-96 for nouveau, HD-5770 for radeon, Intel Ivybridge
with Linux 4.13 and drm-next to fix page flipping.
Fixes: 9d147305b4 ("modesetting: Check if buffer format is supported when flipping")
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
ce2a4313dd