atmel_serial: fix uart/console concurrent access

Strange chars appear on the serial port when a printk and a printf
happens at the same time.  This is caused by the pdc sending chars while
atmel_console_write (called from printk) is executing

Concurent access of uart and console to the same port leads to corrupted
data to be transmitted, so disable tx dma (PDC) while writing to the
console.

Signed-off-by: Marc Pignat <marc.pignat@hevs.ch>
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/serial/atmel_serial.c

@@ -107,6 +107,7 @@
 
 #define UART_PUT_TPR(port,v)	__raw_writel(v, (port)->membase + ATMEL_PDC_TPR)
 #define UART_PUT_TCR(port,v)	__raw_writel(v, (port)->membase + ATMEL_PDC_TCR)
+#define UART_GET_TCR(port)	__raw_readl((port)->membase + ATMEL_PDC_TCR)
 
 static int (*atmel_open_hook)(struct uart_port *);
 static void (*atmel_close_hook)(struct uart_port *);
@@ -1275,13 +1276,18 @@ static void atmel_console_write(struct console *co, const char *s, u_int count)
 {
 	struct uart_port *port = &atmel_ports[co->index].uart;
 	unsigned int status, imr;
+	unsigned int pdc_tx;
 
 	/*
 	 * First, save IMR and then disable interrupts
 	 */
 	imr = UART_GET_IMR(port);
 	UART_PUT_IDR(port, ATMEL_US_RXRDY | ATMEL_US_TXRDY);
 
+	/* Store PDC transmit status and disable it */
+	pdc_tx = UART_GET_PTSR(port) & ATMEL_PDC_TXTEN;
+	UART_PUT_PTCR(port, ATMEL_PDC_TXTDIS);
+
 	uart_console_write(port, s, count, atmel_console_putchar);
 
 	/*
@@ -1291,6 +1297,11 @@ static void atmel_console_write(struct console *co, const char *s, u_int count)
 	do {
 		status = UART_GET_CSR(port);
 	} while (!(status & ATMEL_US_TXRDY));
+
+	/* Restore PDC transmit status */
+	if (pdc_tx)
+		UART_PUT_PTCR(port, ATMEL_PDC_TXTEN);
+
 	/* set interrupts back the way they were */
 	UART_PUT_IER(port, imr);
 }