Am 19.08.2016 um 23:43 schrieb Eric Anholt:
Daniel Vetter <daniel.vetter@xxxxxxxx> writes:
Everyone knows them, except all the new folks joining from the ARM
side haven't lived through all the pain of the past years and are
entirely surprised when I raise this. Definitely time to document
this.
Oh, yes please.
---
Documentation/gpu/drm-uapi.rst | 67 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 67 insertions(+)
diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
index 94876938aef3..a7e3aa27167d 100644
--- a/Documentation/gpu/drm-uapi.rst
+++ b/Documentation/gpu/drm-uapi.rst
@@ -36,6 +36,73 @@ Primary Nodes, DRM Master and Authentication
Open-Source Userspace Requirements
==================================
+The DRM subsystem has stricter requirements on what the userspace side for new
+uAPI needs to look like. This section here explains what exactly those
+requirements are, and why they exist.
+
+The short summary is that any addition of DRM uAPI requires corresponding
+open-sourced userspace patches, and those patches must be reviewed and ready for
+merging into a suitable and canonical upstream project.
+
+GFX devices (both display and render/GPU side) are really complex bits of hardware,
+with userspace and kernel by necessity having to work together really closely.
+The interfaces, for rendering and modesetting must be extremely wide and
I think there should be another comma after "modesetting".
+flexible, and therefore it is almost always impossible to precisely define them
+for every possible corner case. This in turns makes it really practically
"in turn"
+These are fairly steep requirements, but have grown out from years of shared
+pain and experience with uAPI added hastily, and almost always regretted about
+as fast. GFX devices change really fast, requiring a paradigm shift and entire
+new set of uAPI interfaces every few years at least. Together with the Linux
+kernel's guarantee to keep existing userspace running for 10+ years this is
+already rather painful for the DRM subsystem, with multiple different uAPIs for
+the same thing co-existing. If we'd add a few more complete mistakes into the
"If we"
+mix every year it would be entirely unmanagable.
With the little nitpicks (probably) fixed,
Reviewed-by: Eric Anholt <eric@xxxxxxxxxx>
I read through it and can't find anything more to add. So with Eric's
comments fixed the patch is Reviewed-by: Christian König
<christian.koenig@xxxxxxx>.
Additional to that I think with our hybrid stack this is rather
important for AMD. So I'm going to forward it to a few people internally
as well.
Regards,
Christian.
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