When system goes into low power states like SUSPEND_MEM and
HIBERNATION, the hardware IP block may be powered off to reduce
the power consumption. This power down may cause problems on
some imx platforms, because the hardware settings are reset to
its power on default values which may differ from the ones when
it power off. This patch added the dev_pm_ops and implemented
two callbacks: suspend_noirq and resume_noirq, which will save
the necessory hardware parameters right before power down and
recover them before system uses the hardware.

Signed-off-by: Shenwei Wang <redacted>
---
 drivers/tty/serial/imx.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index c8cfa06..acaaa68 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c

@@ -216,6 +216,7 @@ struct imx_port {
 	unsigned int		tx_bytes;
 	unsigned int		dma_tx_nents;
 	wait_queue_head_t	dma_wait;
+	unsigned int            saved_reg[10];
 };
 
 struct imx_port_ucrs {

@@ -1986,6 +1987,58 @@ static int serial_imx_remove(struct platform_device *pdev)
 	return uart_remove_one_port(&imx_reg, &sport->port);
 }
 
+static int imx_serial_port_suspend_noirq(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct imx_port *sport = platform_get_drvdata(pdev);
+
+	/* Save necessary regs */
+	clk_enable(sport->clk_ipg);
+	sport->saved_reg[0] = readl(sport->port.membase + UCR1);
+	sport->saved_reg[1] = readl(sport->port.membase + UCR2);
+	sport->saved_reg[2] = readl(sport->port.membase + UCR3);
+	sport->saved_reg[3] = readl(sport->port.membase + UCR4);
+	sport->saved_reg[4] = readl(sport->port.membase + UFCR);
+	sport->saved_reg[5] = readl(sport->port.membase + UESC);
+	sport->saved_reg[6] = readl(sport->port.membase + UTIM);
+	sport->saved_reg[7] = readl(sport->port.membase + UBIR);
+	sport->saved_reg[8] = readl(sport->port.membase + UBMR);
+	sport->saved_reg[9] = readl(sport->port.membase + IMX21_UTS);
+	clk_disable(sport->clk_ipg);
+
+	pr_debug("0x%p (%d)\r\n", sport->port.membase, sport->port.line);