diff options
Diffstat (limited to 'Documentation/nfc')
| -rw-r--r-- | Documentation/nfc/nfc-hci.txt | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/Documentation/nfc/nfc-hci.txt b/Documentation/nfc/nfc-hci.txt index 320f9336c78..89a339c9b07 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. |