NFC: trf7970a: Recalculate driver timeout values
Some of the timeout values used in the driver
are not long enough to handle worst-case scenarios
so they need to be recalculated.
The time to wait for the FIFO to drain past the
low-watermark is now 20 ms because it can take
around 14.35 ms to send 95 bytes (127 bytes in
full FIFO minus 32 bytes where the low-watermark
interrupt will fire). 95 bytes will take around
14.35 ms at 6.62 kbps (the lowest supported bit
rate used by ISO/IEC 15693) so 20 ms should be a
safe value.
The time to wait before issuing an EOF to complete
an ISO/IEC 15693 write or lock command is 40 ms--
20 ms to drain the FIFO and another 20 ms to ensure
the wait is long enough before sending an EOF.
Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/nfc/trf7970a.c b/drivers/nfc/trf7970a.c
index 22485e7..b67946c 100644
--- a/drivers/nfc/trf7970a.c
+++ b/drivers/nfc/trf7970a.c
@@ -83,6 +83,13 @@
* been received and there isn't an error). The delay is 20 ms since delays
* of ~16 ms have been observed during testing.
*
+ * When transmitting a frame larger than the FIFO size (127 bytes), the
+ * driver will wait 20 ms for the FIFO to drain past the low-watermark
+ * and generate an interrupt. The low-watermark set to 32 bytes so the
+ * interrupt should fire after 127 - 32 = 95 bytes have been sent. At
+ * the lowest possible bit rate (6.62 kbps for 15693), it will take up
+ * to ~14.35 ms so 20 ms is used for the timeout.
+ *
* Type 2 write and sector select commands respond with a 4-bit ACK or NACK.
* Having only 4 bits in the FIFO won't normally generate an interrupt so
* driver enables the '4_bit_RX' bit of the Special Functions register 1
@@ -105,7 +112,9 @@
* Note under Table 1-1 in section 1.6 of
* http://www.ti.com/lit/ug/scbu011/scbu011.pdf, that wait should be at least
* 10 ms for TI Tag-it HF-I tags; however testing has shown that is not long
- * enough. For this reason, the driver waits 20 ms which seems to work
+ * enough so 20 ms is used. So the timer is set to 40 ms - 20 ms to drain
+ * up to 127 bytes in the FIFO at the lowest bit rate plus another 20 ms to
+ * ensure the wait is long enough before sending the EOF. This seems to work
* reliably.
*/
@@ -131,8 +140,8 @@
#define TRF7970A_TX_MAX (4096 - 1)
#define TRF7970A_WAIT_FOR_RX_DATA_TIMEOUT 20
-#define TRF7970A_WAIT_FOR_FIFO_DRAIN_TIMEOUT 3
-#define TRF7970A_WAIT_TO_ISSUE_ISO15693_EOF 20
+#define TRF7970A_WAIT_FOR_FIFO_DRAIN_TIMEOUT 20
+#define TRF7970A_WAIT_TO_ISSUE_ISO15693_EOF 40
/* Guard times for various RF technologies (in us) */
#define TRF7970A_GUARD_TIME_NFCA 5000