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author | Jakub Kicinski <kuba@kernel.org> | 2024-03-22 02:14:13 +0300 |
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committer | Jakub Kicinski <kuba@kernel.org> | 2024-03-22 02:15:08 +0300 |
commit | 537c2e91d3549e5d6020bb0576cf9b54a845255f (patch) | |
tree | c09e8a1b7d733cde19b0c72678c28fb2bc97ff6b /Documentation/usb/functionfs.rst | |
parent | 237bb5f7f7f55ec5f773469a974c61a49c298625 (diff) | |
parent | cba9ffdb9913dfe6be29f049ce920ce451ce7cc4 (diff) | |
download | linux-537c2e91d3549e5d6020bb0576cf9b54a845255f.tar.xz |
Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
Cross-merge networking fixes after downstream PR.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'Documentation/usb/functionfs.rst')
-rw-r--r-- | Documentation/usb/functionfs.rst | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/Documentation/usb/functionfs.rst b/Documentation/usb/functionfs.rst index a3054bea38f3..d05a775bc45b 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. |