Commit 3683a5eb authored by Simon Ser's avatar Simon Ser
Browse files

linux-dmabuf: clarify what mixed valid/INVALID modifiers mean

This commit makes it clear that compositors can send valid modifiers and
DRM_FORMAT_MOD_INVALID for a given format. This means that the compositor
supports both implicit and explicit modifiers. See the warning further
down:

> Warning: It should be an error if the format/modifier pair was not
> advertised with the modifier event. This is not enforced yet because
> some implementations always accept DRM_FORMAT_MOD_INVALID. Also
> version 2 of this protocol does not have the modifier event.

Xwayland already requires compositors to send DRM_FORMAT_MOD_INVALID
for importing buffers with an implicit modifier [1].

In a future protocol version, it would be nice to make it a protocol
error (or at least a soft failure) to use any format/modifier pair that
wasn't advertised. A use-case for this is Vulkan compositors: the Vulkan
DMA-BUF extensions require an explicit modifier and cannot import
buffers which have an implicit modifier.

[1]: https://gitla...
parent 42da2294
Pipeline #293063 passed with stages
in 45 seconds
......@@ -143,6 +143,9 @@
is as if no explicit modifier is specified. The effective modifier
will be derived from the dmabuf.
A compositor that sends valid modifiers and DRM_FORMAT_MOD_INVALID for
a given format supports both explicit modifiers and implicit modifiers.
For the definition of the format and modifier codes, see the
zwp_linux_buffer_params_v1::create and zwp_linux_buffer_params_v1::add
requests.
......
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