serial: MPSC: Remove race between Rx stop & restart

The patch in commit ID f7232056 stops (aborts)
the MPSC's receive engine just before restarting it.  Unfortunately, it
doesn't wait for the abort to complete before restarting it which creates a
race between the abort and the restart.  If the restart occurs first, the
in-progress abort stops it again and the rx engine remains stopped.

Instead, do the abort when the SDMA engine is being stopped.  Make sure to
wait for the abort to complete before continuing.
Signed-off-by: NCarlos Sanchez <carlos.sanchez@gecoinc.com>
Signed-off-by: NMark A. Greer <mgreer@mvista.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/serial/mpsc.c

@@ -1363,8 +1363,6 @@ mpsc_start_rx(struct mpsc_port_info *pi)
 {
 	pr_debug("mpsc_start_rx[%d]: Starting...\n", pi->port.line);
 
-	/* Issue a Receive Abort to clear any receive errors */
-	writel(MPSC_CHR_2_RA, pi->mpsc_base + MPSC_CHR_2);
 	if (pi->rcv_data) {
 		mpsc_enter_hunt(pi);
 		mpsc_sdma_cmd(pi, SDMA_SDCM_ERD);
@@ -1379,6 +1377,20 @@ mpsc_stop_rx(struct uart_port *port)
 
 	pr_debug("mpsc_stop_rx[%d]: Stopping...\n", port->line);
 
+	if (pi->mirror_regs) {
+		writel(pi->MPSC_CHR_2_m | MPSC_CHR_2_RA,
+				pi->mpsc_base + MPSC_CHR_2);
+		/* Erratum prevents reading CHR_2 so just delay for a while */
+		udelay(100);
+	}
+	else {
+		writel(readl(pi->mpsc_base + MPSC_CHR_2) | MPSC_CHR_2_RA,
+			pi->mpsc_base + MPSC_CHR_2);
+
+		while (readl(pi->mpsc_base + MPSC_CHR_2) & MPSC_CHR_2_RA)
+			udelay(10);
+	}
+
 	mpsc_sdma_cmd(pi, SDMA_SDCM_AR);
 	return;
 }