Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+========================
+Multiplane Overlay (MPO)
+========================
+
+.. note:: You will get more from this page if you have already read the
+   'Documentation/gpu/amdgpu/display/dcn-overview.rst'.
+
+
+Multiplane Overlay (MPO) allows for multiple framebuffers to be composited via
+fixed-function hardware in the display controller rather than using graphics or
+compute shaders for composition. This can yield some power savings if it means
+the graphics/compute pipelines can be put into low-power states. In summary,
+MPO can bring the following benefits:
+
+* Decreased GPU and CPU workload - no composition shaders needed, no extra
+  buffer copy needed, GPU can remain idle.
+* Plane independent page flips - No need to be tied to global compositor
+  page-flip present rate, reduced latency, independent timing.
+
+.. note:: Keep in mind that MPO is all about power-saving; if you want to learn
+   more about power-save in the display context, check the link:
+   `Power <https://gitlab.freedesktop.org/pq/color-and-hdr/-/blob/main/doc/power.rst>`__.
+
+Multiplane Overlay is only available using the DRM atomic model. The atomic
+model only uses a single userspace IOCTL for configuring the display hardware
+(modesetting, page-flipping, etc) - drmModeAtomicCommit. To query hardware
+resources and limitations userspace also calls into drmModeGetResources which
+reports back the number of planes, CRTCs, and connectors. There are three types
+of DRM planes that the driver can register and work with:
+
+* ``DRM_PLANE_TYPE_PRIMARY``: Primary planes represent a "main" plane for a
+  CRTC, primary planes are the planes operated upon by CRTC modesetting and
+  flipping operations.
+* ``DRM_PLANE_TYPE_CURSOR``: Cursor planes represent a "cursor" plane for a
+  CRTC. Cursor planes are the planes operated upon by the cursor IOCTLs
+* ``DRM_PLANE_TYPE_OVERLAY``: Overlay planes represent all non-primary,
+  non-cursor planes. Some drivers refer to these types of planes as "sprites"
+  internally.
+
+To illustrate how it works, let's take a look at a device that exposes the
+following planes to userspace:
+
+* 4 Primary planes (1 per CRTC).
+* 4 Cursor planes (1 per CRTC).
+* 1 Overlay plane (shared among CRTCs).
+
+.. note:: Keep in mind that different ASICs might expose other numbers of
+   planes.
+
+For this hardware example, we have 4 pipes (if you don't know what AMD pipe
+means, look at 'Documentation/gpu/amdgpu/display/dcn-overview.rst', section
+"AMD Hardware Pipeline"). Typically most AMD devices operate in a pipe-split
+configuration for optimal single display output (e.g., 2 pipes per plane).
+
+A typical MPO configuration from userspace - 1 primary + 1 overlay on a single
+display - will see 4 pipes in use, 2 per plane.
+
+At least 1 pipe must be used per plane (primary and overlay), so for this
+hypothetical hardware that we are using as an example, we have an absolute
+limit of 4 planes across all CRTCs. Atomic commits will be rejected for display
+configurations using more than 4 planes. Again, it is important to stress that
+every DCN has different restrictions; here, we are just trying to provide the
+concept idea.
+
+Plane Restrictions
+==================
+
+AMDGPU imposes restrictions on the use of DRM planes in the driver.
+
+Atomic commits will be rejected for commits which do not follow these
+restrictions:
+
+* Overlay planes must be in ARGB8888 or XRGB8888 format
+* Planes cannot be placed outside of the CRTC destination rectangle
+* Planes cannot be downscaled more than 1/4x of their original size
+* Planes cannot be upscaled more than 16x of their original size
+
+Not every property is available on every plane:
+
+* Only primary planes have color-space and non-RGB format support
+* Only overlay planes have alpha blending support
+
+Cursor Restrictions
+===================
+
+Before we start to describe some restrictions around cursor and MPO, see the
+below image:
+
+.. kernel-figure:: mpo-cursor.svg
+
+The image on the left side represents how DRM expects the cursor and planes to
+be blended. However, AMD hardware handles cursors differently, as you can see
+on the right side; basically, our cursor cannot be drawn outside its associated
+plane as it is being treated as part of the plane. Another consequence of that
+is that cursors inherit the color and scale from the plane.
+
+As a result of the above behavior, do not use legacy API to set up the cursor
+plane when working with MPO; otherwise, you might encounter unexpected
+behavior.
+
+In short, AMD HW has no dedicated cursor planes. A cursor is attached to
+another plane and therefore inherits any scaling or color processing from its
+parent plane.
+
+Use Cases
+=========
+
+Picture-in-Picture (PIP) playback - Underlay strategy
+-----------------------------------------------------
+
+Video playback should be done using the "primary plane as underlay" MPO
+strategy. This is a 2 planes configuration:
+
+* 1 YUV DRM Primary Plane (e.g. NV12 Video)
+* 1 RGBA DRM Overlay Plane (e.g. ARGB8888 desktop). The compositor should
+  prepare the framebuffers for the planes as follows:
+  - The overlay plane contains general desktop UI, video player controls, and video subtitles
+  - Primary plane contains one or more videos
+
+.. note:: Keep in mind that we could extend this configuration to more planes,
+   but that is currently not supported by our driver yet (maybe if we have a
+   userspace request in the future, we can change that).
+
+See below a single-video example:
+
+.. kernel-figure:: single-display-mpo.svg
+
+.. note:: We could extend this behavior to more planes, but that is currently
+   not supported by our driver.
+
+The video buffer should be used directly for the primary plane. The video can
+be scaled and positioned for the desktop using the properties: CRTC_X, CRTC_Y,
+CRTC_W, and CRTC_H. The primary plane should also have the color encoding and
+color range properties set based on the source content:
+
+* ``COLOR_RANGE``, ``COLOR_ENCODING``
+
+The overlay plane should be the native size of the CRTC. The compositor must
+draw a transparent cutout for where the video should be placed on the desktop
+(i.e., set the alpha to zero). The primary plane video will be visible through
+the underlay. The overlay plane's buffer may remain static while the primary
+plane's framebuffer is used for standard double-buffered playback.
+
+The compositor should create a YUV buffer matching the native size of the CRTC.
+Each video buffer should be composited onto this YUV buffer for direct YUV
+scanout. The primary plane should have the color encoding and color range
+properties set based on the source content: ``COLOR_RANGE``,
+``COLOR_ENCODING``. However, be mindful that the source color space and
+encoding match for each video since it affect the entire plane.
+
+The overlay plane should be the native size of the CRTC. The compositor must
+draw a transparent cutout for where each video should be placed on the desktop
+(i.e., set the alpha to zero). The primary plane videos will be visible through
+the underlay. The overlay plane's buffer may remain static while compositing
+operations for video playback will be done on the video buffer.
+
+This kernel interface is validated using IGT GPU Tools. The following tests can
+be run to validate positioning, blending, scaling under a variety of sequences
+and interactions with operations such as DPMS and S3:
+
+- ``kms_plane@plane-panning-bottom-right-pipe-*-planes``
+- ``kms_plane@plane-panning-bottom-right-suspend-pipe-*-``
+- ``kms_plane@plane-panning-top-left-pipe-*-``
+- ``kms_plane@plane-position-covered-pipe-*-``
+- ``kms_plane@plane-position-hole-dpms-pipe-*-``
+- ``kms_plane@plane-position-hole-pipe-*-``
+- ``kms_plane_multiple@atomic-pipe-*-tiling-``
+- ``kms_plane_scaling@pipe-*-plane-scaling``
+- ``kms_plane_alpha_blend@pipe-*-alpha-basic``
+- ``kms_plane_alpha_blend@pipe-*-alpha-transparant-fb``
+- ``kms_plane_alpha_blend@pipe-*-alpha-opaque-fb``
+- ``kms_plane_alpha_blend@pipe-*-constant-alpha-min``
+- ``kms_plane_alpha_blend@pipe-*-constant-alpha-mid``
+- ``kms_plane_alpha_blend@pipe-*-constant-alpha-max``
+
+Multiple Display MPO
+--------------------
+
+AMDGPU supports display MPO when using multiple displays; however, this feature
+behavior heavily relies on the compositor implementation. Keep in mind that
+usespace can define different policies. For example, some OSes can use MPO to
+protect the plane that handles the video playback; notice that we don't have
+many limitations for a single display. Nonetheless, this manipulation can have
+many more restrictions for a multi-display scenario. The below example shows a
+video playback in the middle of two displays, and it is up to the compositor to
+define a policy on how to handle it:
+
+.. kernel-figure:: multi-display-hdcp-mpo.svg
+
+Let's discuss some of the hardware limitations we have when dealing with
+multi-display with MPO.
+
+Limitations
+~~~~~~~~~~~
+
+For simplicity's sake, for discussing the hardware limitation, this
+documentation supposes an example where we have two displays and video playback
+that will be moved around different displays.
+
+* **Hardware limitations**
+
+From the DCN overview page, each display requires at least one pipe and each
+MPO plane needs another pipe. As a result, when the video is in the middle of
+the two displays, we need to use 2 pipes. See the example below where we avoid
+pipe split:
+
+- 1 display (1 pipe) + MPO (1 pipe), we will use two pipes
+- 2 displays (2 pipes) + MPO (1-2 pipes); we will use 4 pipes. MPO in the
+  middle of both displays needs 2 pipes.
+- 3 Displays (3 pipes) + MPO (1-2 pipes), we need 5 pipes.
+
+If we use MPO with multiple displays, the userspace has to decide to enable
+multiple MPO by the price of limiting the number of external displays supported
+or disable it in favor of multiple displays; it is a policy decision. For
+example:
+
+* When ASIC has 3 pipes, AMD hardware can NOT support 2 displays with MPO
+* When ASIC has 4 pipes, AMD hardware can NOT support 3 displays with MPO
+
+Let's briefly explore how userspace can handle these two display configurations
+on an ASIC that only supports three pipes. We can have:
+
+.. kernel-figure:: multi-display-hdcp-mpo-less-pipe-ex.svg
+
+- Total pipes are 3
+- User lights up 2 displays (2 out of 3 pipes are used)
+- User launches video (1 pipe used for MPO)
+- Now, if the user moves the video in the middle of 2 displays, one part of the
+  video won't be MPO since we have used 3/3 pipes.
+
+* **Scaling limitation**
+
+MPO cannot handle scaling less than 0.25 and more than x16. For example:
+
+If 4k video (3840x2160) is playing in windowed mode, the physical size of the
+window cannot be smaller than (960x540).
+
+.. note:: These scaling limitations might vary from ASIC to ASIC.
+
+* **Size Limitation**
+
+The minimum MPO size is 12px.