serial: mvebu-uart: initialize over sampling stack register

The baudrate derivation relies on the state of the programmable over
sampling stack (OSAMP register) being empty, while never initializing
it.

Set all the fields of this register to 0 (except reserved areas) to
ensure a x16 divisor, as assumed by the driver.

The suspend/resume callbacks are untouched because they already
save/restore correctly this register.

Suggested-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-uart.c
index df6e4d8cdbd6094da85a24bc992176145925f13c..231f751d1ef48b42e4a9820c73408242862035e9 100644 (file)
--- a/drivers/tty/serial/mvebu-uart.c
+++ b/drivers/tty/serial/mvebu-uart.c
@@ -73,6 +73,7 @@
 
 #define UART_OSAMP             0x14
 #define  OSAMP_DEFAULT_DIVISOR 16
+#define  OSAMP_DIVISORS_MASK   0x3F3F3F3F
 
 #define MVEBU_NR_UARTS         2
 
@@ -446,7 +447,7 @@ static int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
 {
        struct mvebu_uart *mvuart = to_mvuart(port);
        unsigned int d_divisor, m_divisor;
-       u32 brdv;
+       u32 brdv, osamp;
 
        if (IS_ERR(mvuart->clk))
                return -PTR_ERR(mvuart->clk);
@@ -469,6 +470,10 @@ static int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
        brdv |= d_divisor;
        writel(brdv, port->membase + UART_BRDV);
 
+       osamp = readl(port->membase + UART_OSAMP);
+       osamp &= ~OSAMP_DIVISORS_MASK;
+       writel(osamp, port->membase + UART_OSAMP);
+
        return 0;
 }