NFC: trf7970a: Reread FIFO Status Register when draining FIFO

Receiving an interrupt whose Interrupt Status Register
value has only the SRX bit set is supposed to mean that
all of the data from the tag has been received.  That
turns out to not be true so we need to reread the FIFO
Status Register to tell if there are any new bytes in
the FIFO.  If there are, continue receiving them; if
there aren't, assume that the receive is complete and
pass the data up.
Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/nfc/trf7970a.c

@@ -648,6 +648,21 @@ static void trf7970a_drain_fifo(struct trf7970a *trf, u8 status)
 		status = TRF7970A_IRQ_STATUS_SRX;
 	} else {
 		trf->state = TRF7970A_ST_WAIT_FOR_RX_DATA_CONT;
+
+		ret = trf7970a_read(trf, TRF7970A_FIFO_STATUS, &fifo_bytes);
+		if (ret) {
+			trf7970a_send_err_upstream(trf, ret);
+			return;
+		}
+
+		fifo_bytes &= ~TRF7970A_FIFO_STATUS_OVERFLOW;
+
+		/* If there are bytes in the FIFO, set status to '0' so
+		 * the if stmt below doesn't fire and the driver will wait
+		 * for the trf7970a to generate another RX interrupt.
+		 */
+		if (fifo_bytes)
+			status = 0;
 	}
 
 no_rx_data: