hid_locate: do not ignore constant items.
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Authored by wulf on Dec 23 2020, 9:13 PM.

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rG3f2709285421: hid_locate: do not ignore constant items.

Summary

hid_locate() currently skips all HID items which tagged as constant,
i.e. bit 0 of main item data is set to 1. See p.6.2.2.4 of hid1_11.pdf [1].
It looks like such an items are treated as padding, but that is wrong. They
can be a features, see: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=232040

As p.6.2.2.9 of hid1_11.pdf clearly states: "Reports can be padded to
byte-align fields by declaring the appropriately sized main item and not
declaring a usage for the main item.", we should remove check for constant
from hid_locate(). Comparing of item usage is enough.

[1] https://www.usb.org/sites/default/files/documents/hid1_11.pdf

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rG FreeBSD src repository

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wulf requested review of this revision.Dec 23 2020, 9:13 PM

wulf created this revision.

Don't forget to MFC.

This revision is now accepted and ready to land.Dec 24 2020, 11:29 AM

Really, Summary is slightly misleading. Const items can be used as byte-padding items too, but we can't blindly count on it. Will try to write it better.

emaste mentioned this in D27777: Separate HID support from USB subsystem and import sysutils/iichid into the base..Dec 30 2020, 5:13 PM

Closed by commit rG3f2709285421: hid_locate: do not ignore constant items. (authored by wulf_cicgroup.ru, committed by wulf). · Explain WhyJan 7 2021, 11:21 PM

This revision was automatically updated to reflect the committed changes.

wulf added a commit: rG3f2709285421: hid_locate: do not ignore constant items..