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usb: gadget: f_fs: Document eventfd effect on descriptor format.

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When FUNCTIONFS_EVENTFD flag is set, __ffs_data_got_descs reads a 32bits,
little-endian value right after the fixed structure header, and passes it
to eventfd_ctx_fdget. Document this.

Also, rephrase a comment to be affirmative about the role of string
descriptor at index 0. Ref: USB 2.0 spec paragraph "9.6.7 String", and
also checked to still be current in USB 3.0 spec paragraph "9.6.9 String".

Signed-off-by: Vincent Pelletier <plr.vincent@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
This commit is contained in:
Vincent Pelletier
2016-12-15 12:47:41 +00:00
committed by Felipe Balbi
parent 7e4da3fcf7
commit 96a420d2d3
2 changed files with 3 additions and 2 deletions
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include/uapi/linux/usb/functionfs.h
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@@ -93,6 +93,7 @@ struct usb_ext_prop_desc {
* | 0 | magic | LE32 | FUNCTIONFS_DESCRIPTORS_MAGIC_V2 |
* | 4 | length | LE32 | length of the whole data chunk |
* | 8 | flags | LE32 | combination of functionfs_flags |
* | | eventfd | LE32 | eventfd file descriptor |
* | | fs_count | LE32 | number of full-speed descriptors |
* | | hs_count | LE32 | number of high-speed descriptors |
* | | ss_count | LE32 | number of super-speed descriptors |