path: root/Documentation/nfc
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authorEric Lapuyade <eric.lapuyade@intel.com>2012-05-03 11:49:30 +0200
committerJohn W. Linville <linville@tuxdriver.com>2012-07-09 16:42:11 -0400
commit36516268fd372294f5f4f26e0538ee70a1b5b9e7 (patch)
tree0e589dd20c94f5600097f559123483a52b91b626 /Documentation/nfc
parent9eb334ac1709e8f135af341ce1dd0e6b4449c6d3 (diff)
NFC: Error management documentation
Signed-off-by: Eric Lapuyade <eric.lapuyade@intel.com> Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Diffstat (limited to 'Documentation/nfc')
1 files changed, 33 insertions, 0 deletions
diff --git a/Documentation/nfc/nfc-hci.txt b/Documentation/nfc/nfc-hci.txt
index 320f9336c781..89a339c9b079 100644
--- a/Documentation/nfc/nfc-hci.txt
+++ b/Documentation/nfc/nfc-hci.txt
@@ -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.