[PATCH 5/8] serial: imx: save and restore context in the suspend path

[Eduardo Valentin <edubezval@gmail.com>]

This change teaches the imx serial driver to save its
context and restore it across suspend and resume path.
To do so, it introduces serial_imx_restore_context()
and serial_imx_save_context() functions. They use
a shadow set of registers to save key registers
and restore them accordingly. These functions can
be reused on other situations, when the device
context is lost.

Cc: Fabio Stevam <festevam@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>
---
 drivers/tty/serial/imx.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index a03855d..494b182 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -217,6 +217,8 @@ struct imx_port {
 	unsigned int		tx_bytes;
 	unsigned int		dma_tx_nents;
 	wait_queue_head_t	dma_wait;
+	unsigned int		saved_reg[8];
+	bool			context_saved;
 };
 
 struct imx_port_ucrs {
@@ -1803,6 +1805,36 @@ static struct uart_driver imx_reg = {
 	.cons           = IMX_CONSOLE,
 };
 
+static void serial_imx_restore_context(struct imx_port *sport)
+{
+	if (!sport->context_saved)
+		return;
+
+	writel(sport->saved_reg[4], sport->port.membase + UFCR);
+	writel(sport->saved_reg[5], sport->port.membase + UBIR);
+	writel(sport->saved_reg[6], sport->port.membase + UBMR);
+	writel(sport->saved_reg[7], sport->port.membase + IMX21_UTS);
+	writel(sport->saved_reg[0], sport->port.membase + UCR1);
+	writel(sport->saved_reg[1] | 0x1, sport->port.membase + UCR2);
+	writel(sport->saved_reg[2], sport->port.membase + UCR3);
+	writel(sport->saved_reg[3], sport->port.membase + UCR4);
+	sport->context_saved = false;
+}
+
+static void serial_imx_save_context(struct imx_port *sport)
+{
+	/* Save necessary regs */
+	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 + UBIR);
+	sport->saved_reg[6] = readl(sport->port.membase + UBMR);
+	sport->saved_reg[7] = readl(sport->port.membase + IMX21_UTS);
+	sport->context_saved = true;
+}
+
 static void serial_imx_enable_wakeup(struct imx_port *sport, bool on)
 {
 	unsigned int val;
@@ -1826,6 +1858,7 @@ static int serial_imx_suspend(struct device *dev)
 {
 	struct imx_port *sport = dev_get_drvdata(dev);
 
+	serial_imx_save_context(sport);
 	/* enable wakeup from i.MX UART */
 	serial_imx_enable_wakeup(sport, true);
 
@@ -1841,6 +1874,7 @@ static int serial_imx_resume(struct device *dev)
 	/* disable wakeup from i.MX UART */
 	serial_imx_enable_wakeup(sport, false);
 
+	serial_imx_restore_context(sport);
 	uart_resume_port(&imx_reg, &sport->port);
 
 	return 0;
-- 
2.5.0