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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-08-07 13:11:27 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-08-07 13:11:27 +0000
commit34996e42f82bfd60bc2c191e5cae3c6ab233ec6c (patch)
tree62db60558cbf089714b48daeabca82bf2b20b20e /Documentation/usb
parentAdding debian version 6.8.12-1. (diff)
downloadlinux-34996e42f82bfd60bc2c191e5cae3c6ab233ec6c.tar.xz
linux-34996e42f82bfd60bc2c191e5cae3c6ab233ec6c.zip
Merging upstream version 6.9.7.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/usb')
-rw-r--r--Documentation/usb/functionfs.rst36
-rw-r--r--Documentation/usb/gadget-testing.rst8
2 files changed, 44 insertions, 0 deletions
diff --git a/Documentation/usb/functionfs.rst b/Documentation/usb/functionfs.rst
index a3054bea38..d05a775bc4 100644
--- a/Documentation/usb/functionfs.rst
+++ b/Documentation/usb/functionfs.rst
@@ -2,6 +2,9 @@
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
@@ -66,3 +69,36 @@ have been written to their ep0's.
Conversely, the gadget is unregistered after the first USB function
closes its 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.
+
+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.
diff --git a/Documentation/usb/gadget-testing.rst b/Documentation/usb/gadget-testing.rst
index 077dfac7ed..b086c7ab72 100644
--- a/Documentation/usb/gadget-testing.rst
+++ b/Documentation/usb/gadget-testing.rst
@@ -206,6 +206,14 @@ the standard procedure for using FunctionFS (mount it, run the userspace
process which implements the function proper). The gadget should be enabled
by writing a suitable string to usb_gadget/<gadget>/UDC.
+The FFS function provides just one attribute in its function directory:
+
+ ready
+
+The attribute is read-only and signals if the function is ready (1) to be
+used, E.G. if userspace has written descriptors and strings to ep0, so
+the gadget can be enabled.
+
Testing the FFS function
------------------------