drm/amd/display: Try RGB before YCbCr 4:4:4 in stream validationgrafted

amdgpu_dm_create_validate_stream_for_sink() walks encoding_order[] and
uses the first encoding that validates. YCbCr 4:4:4 is listed before
RGB, so an HDMI sink that advertises 4:4:4 gets YCbCr 4:4:4 whenever the
"color format" property is left at AUTO, even though RGB fits the same
link.

That contradicts the documented AUTO behaviour for HDMI in enum
drm_connector_color_format (RGB, falling back to YCbCr 4:2:0 only when
the bandwidth is not available or the mode is 4:2:0-only), which the
amdgpu implementation of the property also describes. It also leaves
the "Broadcast RGB" property without effect on such sinks, since the
quantization range it selects only applies to RGB output.

Try RGB first. The mask still holds every encoding the sink supports,
so a mode that cannot carry RGB falls back exactly as before.

For reference, v7.2 picked RGB here unless YCbCr 4:4:4 was forced
through debugfs, while earlier kernels picked YCbCr 4:4:4 for any HDMI
sink that advertised it.

Fixes: 0b0ff65d3ca1 ("drm/amd/display: Refactor stream validation")
Suggested-by: Adolfo Rodrigues <adolfotregosa@gmail.com>
Assisted-by: Claude Code:claude-fable-5-1
Signed-off-by: Adrian Betschart <adrian.betschart@cinemaone.ch>
Reviewed-by: Fangzhi Zuo <jerry.zuo@amd.com>
Tested-by: Adolfo Rodrigues <adolfotregosa@gmail.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 7de432bc753133764dc40d37f9388da56de251e7)

1 files changed, 186 insertions, 0 deletions

diff --git a/Documentation/usb/functionfs.rst b/Documentation/usb/functionfs.rst
new file mode 100644
index 000000000..b189cf562
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+++ b/Documentation/usb/functionfs.rst
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+====================
+How FunctionFS works
+====================
+
+Overview
+========
+
+From kernel point of view it is just a composite function with some
+unique behaviour.  It may be added to an USB configuration only after
+the user space driver has registered by writing descriptors and
+strings (the user space program has to provide the same information
+that kernel level composite functions provide when they are added to
+the configuration).
+
+This in particular means that the composite initialisation functions
+may not be in init section (ie. may not use the __init tag).
+
+From user space point of view it is a file system which when
+mounted provides an "ep0" file.  User space driver need to
+write descriptors and strings to that file.  It does not need
+to worry about endpoints, interfaces or strings numbers but
+simply provide descriptors such as if the function was the
+only one (endpoints and strings numbers starting from one and
+interface numbers starting from zero).  The FunctionFS changes
+them as needed also handling situation when numbers differ in
+different configurations.
+
+For more information about FunctionFS descriptors see :doc:`functionfs-desc`
+
+When descriptors and strings are written "ep#" files appear
+(one for each declared endpoint) which handle communication on
+a single endpoint.  Again, FunctionFS takes care of the real
+numbers and changing of the configuration (which means that
+"ep1" file may be really mapped to (say) endpoint 3 (and when
+configuration changes to (say) endpoint 2)).  "ep0" is used
+for receiving events and handling setup requests.
+
+When all files are closed the function disables itself.
+
+What I also want to mention is that the FunctionFS is designed in such
+a way that it is possible to mount it several times so in the end
+a gadget could use several FunctionFS functions. The idea is that
+each FunctionFS instance is identified by the device name used
+when mounting.
+
+One can imagine a gadget that has an Ethernet, MTP and HID interfaces
+where the last two are implemented via FunctionFS.  On user space
+level it would look like this::
+
+  $ insmod g_ffs.ko idVendor=<ID> iSerialNumber=<string> functions=mtp,hid
+  $ mkdir /dev/ffs-mtp && mount -t functionfs mtp /dev/ffs-mtp
+  $ ( cd /dev/ffs-mtp && mtp-daemon ) &
+  $ mkdir /dev/ffs-hid && mount -t functionfs hid /dev/ffs-hid
+  $ ( cd /dev/ffs-hid && hid-daemon ) &
+
+On kernel level the gadget checks ffs_data->dev_name to identify
+whether its FunctionFS is designed for MTP ("mtp") or HID ("hid").
+
+If no "functions" module parameters is supplied, the driver accepts
+just one function with any name.
+
+When "functions" module parameter is supplied, only functions
+with listed names are accepted. In particular, if the "functions"
+parameter's value is just a one-element list, then the behaviour
+is similar to when there is no "functions" at all; however,
+only a function with the specified name is accepted.
+
+The gadget is registered only after all the declared function
+filesystems have been mounted and USB descriptors of all functions
+have been written to their ep0's.
+
+Conversely, the gadget is unregistered after the first USB function
+closes its endpoints.
+
+Endpoint IOCTLs
+===============
+
+FunctionFS supports additional IOCTLs that can be performed on data endpoints
+(ie. not ep0). For a full list of these IOCTLs, please refer to the documentation
+in ``include/uapi/linux/usb/functionfs.h``.
+
+One such IOCTL is:
+
+  ``FUNCTIONFS_ENDPOINT_ENABLE_ZLP(__u32 *)``
+    Enable or disable automatic zero-length packet (ZLP) appending for the
+    endpoint. The argument is a pointer to a __u32: 0 to disable, non-zero to
+    enable. When enabled, the kernel will automatically append a ZLP at the end
+    of a transfer if the payload length is an exact multiple of the endpoint's
+    max packet size. This is useful for compatibility with legacy protocols
+    which require automatic ZLP appending to data written from userspace. This
+    IOCTL can only be used on IN endpoints. It can be called at any time after
+    the FunctionFS instance is active, even before the host has connected or
+    enabled the endpoint. Returns zero on success, or a negative errno value on
+    error:
+
+    * ``-ENODEV``: The FunctionFS instance is not active.
+    * ``-EINVAL``: The endpoint is not an IN endpoint.
+    * ``-EFAULT``: Invalid user space pointer for the argument.
+
+RW Proxy Endpoints
+==================
+
+If the ``FUNCTIONFS_RW_PROXY_EPS`` flag is passed in the descriptor header
+(requires ``FUNCTIONFS_DESCRIPTORS_MAGIC_V2``), FunctionFS will provision a
+bidirectional rw_proxy file descriptor (e.g., "ep1_rw") alongside each pair
+of IN and OUT endpoints. The rw_proxy file aliases the underlying hardware
+endpoints, allowing userspace to use a single file descriptor for both reading
+(OUT) and writing (IN).
+
+This flag requires the total number of hardware endpoints to be an even number.
+FunctionFS will automatically walk the provided endpoints and group them into
+adjacent pairs (e.g., ep1 and ep2 form the first pair, ep3 and ep4 form the
+second pair). Each pair must consist of exactly one IN endpoint and one OUT
+endpoint.
+
+For each valid pair, a rw_proxy file is created and named after the first
+endpoint in the pair with a "_rw" suffix. For example, if ep1 and ep2 are
+paired, a rw_proxy file named "ep1_rw" is created. If ep3 and ep4 are paired,
+"ep3_rw" is created.
+
+If the ``FUNCTIONFS_VIRTUAL_ADDR`` flag is also enabled, the endpoints will be
+named using their physical endpoint address in hexadecimal instead of their
+index. RW proxy files will inherit this naming convention. For example, if the
+first endpoint of a pair maps to address 0x02, the rw_proxy file will be
+named "ep02_rw".
+
+When this flag is enabled, userspace has the choice of performing data transfers
+via the single rw_proxy file descriptor or the two base file descriptors. The
+rw_proxy file descriptor acts as a pure VFS alias that proxies all operations
+directly to the underlying base file descriptors.
+
+Because it is a pure proxy, there are no data races or buffer corruptions if
+userspace uses both the rw_proxy endpoint and the base endpoints concurrently.
+The native mutexes of the base endpoints perfectly serialize all concurrent
+transfers. However, userspace should generally pick one method and stick to it
+to avoid interleaving its own data stream.
+
+- **IOCTLs (Clear Halt, etc.):** RW proxy endpoints do not support IOCTLs and
+  will return ``-ENOTTY``. To clear a host-initiated halt, userspace must issue
+  the ``FUNCTIONFS_CLEAR_HALT`` ioctl directly on the corresponding base
+  endpoint file descriptor.
+- **Intentional Stalls:** The traditional mechanism for intentionally halting an
+  endpoint by issuing a reverse-direction data operation (e.g., attempting to
+  read from an IN endpoint) continues to work, but it must be issued on the
+  base endpoint. RW proxy endpoints cannot be used to trigger a stall because
+  they are fully bidirectional.
+
+Note that DMABUF data transfers (``FUNCTIONFS_DMABUF_TRANSFER``) are unsupported
+via the rw_proxy endpoint because it does not support IOCTLs. If DMABUF
+transfers are required, users must use the standard base endpoints.
+DMABUF interface
+================
+
+FunctionFS additionally supports a DMABUF based interface, where the
+userspace can attach DMABUF objects (externally created) to an endpoint,
+and subsequently use them for data transfers.
+
+Note: The DMABUF interface is unsupported on rw_proxy endpoints. See
+the RW Proxy Endpoints section for details on using DMABUF alongside
+the ``FUNCTIONFS_RW_PROXY_EPS`` flag.
+
+A userspace application can then use this interface to share DMABUF
+objects between several interfaces, allowing it to transfer data in a
+zero-copy fashion, for instance between IIO and the USB stack.
+
+As part of this interface, three new IOCTLs have been added. These three
+IOCTLs have to be performed on a data endpoint (ie. not ep0). They are:
+
+  ``FUNCTIONFS_DMABUF_ATTACH(int)``
+    Attach the DMABUF object, identified by its file descriptor, to the
+    data endpoint. Returns zero on success, and a negative errno value
+    on error.
+
+  ``FUNCTIONFS_DMABUF_DETACH(int)``
+    Detach the given DMABUF object, identified by its file descriptor,
+    from the data endpoint. Returns zero on success, and a negative
+    errno value on error. Note that closing the endpoint's file
+    descriptor will automatically detach all attached DMABUFs.
+
+  ``FUNCTIONFS_DMABUF_TRANSFER(struct usb_ffs_dmabuf_transfer_req *)``
+    Enqueue the previously attached DMABUF to the transfer queue.
+    The argument is a structure that packs the DMABUF's file descriptor,
+    the size in bytes to transfer (which should generally correspond to
+    the size of the DMABUF), and a 'flags' field which is unused
+    for now. Returns zero on success, and a negative errno value on
+    error.