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NFC: Error management documentation 

Signed-off-by: Eric Lapuyade <eric.lapuyade@intel.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
This commit is contained in:
Eric Lapuyade 2012-05-03 11:49:30 +02:00 committed by John W. Linville
parent 9eb334ac17
commit 36516268fd
1 changed files with 33 additions and 0 deletions
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33
Documentation/nfc/nfc-hci.txt
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@ -178,3 +178,36 @@ ANY_GET_PARAMETER to the reader A gate to get information on the target
that was discovered).
Typically, such an event will be propagated to NFC Core from MSGRXWQ context.
Error management
----------------
Errors that occur synchronously with the execution of an NFC Core request are
simply returned as the execution result of the request. These are easy.
Errors that occur asynchronously (e.g. in a background protocol handling thread)
must be reported such that upper layers don't stay ignorant that something
went wrong below and know that expected events will probably never happen.
Handling of these errors is done as follows:
- driver (pn544) fails to deliver an incoming frame: it stores the error such
that any subsequent call to the driver will result in this error. Then it calls
the standard nfc_shdlc_recv_frame() with a NULL argument to report the problem
above. shdlc stores a EREMOTEIO sticky status, which will trigger SMW to
report above in turn.
- SMW is basically a background thread to handle incoming and outgoing shdlc
frames. This thread will also check the shdlc sticky status and report to HCI
when it discovers it is not able to run anymore because of an unrecoverable
error that happened within shdlc or below. If the problem occurs during shdlc
connection, the error is reported through the connect completion.
- HCI: if an internal HCI error happens (frame is lost), or HCI is reported an
error from a lower layer, HCI will either complete the currently executing
command with that error, or notify NFC Core directly if no command is executing.
- NFC Core: when NFC Core is notified of an error from below and polling is
active, it will send a tag discovered event with an empty tag list to the user
space to let it know that the poll operation will never be able to detect a tag.
If polling is not active and the error was sticky, lower levels will return it
at next invocation.