[RFC PATCH v2 2/2] serial: sc16is7xx: fix regression with GPIO configuration

[Hugo Villeneuve]

From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>

Commit 679875d1d880 ("sc16is7xx: Separate GPIOs from modem control lines")
and commit 21144bab4f11 ("sc16is7xx: Handle modem status lines")
changed the function of the GPIOs pins to act as modem control
lines without any possibility of selecting GPIO function.

As a consequence, applications that depends on GPIO lines configured
by default as GPIO pins no longer work as expected.

Also, the change to select modem control lines function was done only
for channel A of dual UART variants (752/762). This was not documented
in the log message.

This new patch allows to specify GPIO or modem control line function
in the device tree, and for each of the ports (A or B).

This is done by using the new device-tree property named
"modem-control-line-ports" (property added in separate patch).

Boards that need to have GPIOS configured as modem control lines
should add that property to their device tree. Here is a list of
boards using the sc16is7xx driver in their device tree and that may
need to be modified:
    arm64/boot/dts/freescale/fsl-ls1012a-frdm.dts
    mips/boot/dts/ingenic/cu1830-neo.dts
    mips/boot/dts/ingenic/cu1000-neo.dts

Fixes: 679875d1d880 ("sc16is7xx: Separate GPIOs from modem control lines")
Fixes: 21144bab4f11 ("sc16is7xx: Handle modem status lines")
Signed-off-by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
---
v1 -> v2: Rebase because original patch did not apply properly
          Add git base-commit

 drivers/tty/serial/sc16is7xx.c | 42 ++++++++++++++++++++--------------
 1 file changed, 25 insertions(+), 17 deletions(-)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index abad091baeea..4e3d2325ef6e 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -236,7 +236,8 @@
 
 /* IOControl register bits (Only 750/760) */
 #define SC16IS7XX_IOCONTROL_LATCH_BIT	(1 << 0) /* Enable input latching */
-#define SC16IS7XX_IOCONTROL_MODEM_BIT	(1 << 1) /* Enable GPIO[7:4] as modem pins */
+#define SC16IS7XX_IOCONTROL_MODEM_A_BIT	(1 << 1) /* Enable GPIO[7:4] as modem A pins */
+#define SC16IS7XX_IOCONTROL_MODEM_B_BIT	(1 << 2) /* Enable GPIO[3:0] as modem B pins */
 #define SC16IS7XX_IOCONTROL_SRESET_BIT	(1 << 3) /* Software Reset */
 
 /* EFCR register bits */
@@ -306,7 +307,6 @@ struct sc16is7xx_devtype {
 	char	name[10];
 	int	nr_gpio;
 	int	nr_uart;
-	int	has_mctrl;
 };
 
 #define SC16IS7XX_RECONF_MD		(1 << 0)
@@ -447,35 +447,30 @@ static const struct sc16is7xx_devtype sc16is74x_devtype = {
 	.name		= "SC16IS74X",
 	.nr_gpio	= 0,
 	.nr_uart	= 1,
-	.has_mctrl	= 0,
 };
 
 static const struct sc16is7xx_devtype sc16is750_devtype = {
 	.name		= "SC16IS750",
-	.nr_gpio	= 4,
+	.nr_gpio	= 8,
 	.nr_uart	= 1,
-	.has_mctrl	= 1,
 };
 
 static const struct sc16is7xx_devtype sc16is752_devtype = {
 	.name		= "SC16IS752",
-	.nr_gpio	= 0,
+	.nr_gpio	= 8,
 	.nr_uart	= 2,
-	.has_mctrl	= 1,
 };
 
 static const struct sc16is7xx_devtype sc16is760_devtype = {
 	.name		= "SC16IS760",
-	.nr_gpio	= 4,
+	.nr_gpio	= 8,
 	.nr_uart	= 1,
-	.has_mctrl	= 1,
 };
 
 static const struct sc16is7xx_devtype sc16is762_devtype = {
 	.name		= "SC16IS762",
-	.nr_gpio	= 0,
+	.nr_gpio	= 8,
 	.nr_uart	= 2,
-	.has_mctrl	= 1,
 };
 
 static bool sc16is7xx_regmap_volatile(struct device *dev, unsigned int reg)
@@ -1456,12 +1451,6 @@ static int sc16is7xx_probe(struct device *dev,
 				     SC16IS7XX_EFCR_RXDISABLE_BIT |
 				     SC16IS7XX_EFCR_TXDISABLE_BIT);
 
-		/* Use GPIO lines as modem status registers */
-		if (devtype->has_mctrl)
-			sc16is7xx_port_write(&s->p[i].port,
-					     SC16IS7XX_IOCONTROL_REG,
-					     SC16IS7XX_IOCONTROL_MODEM_BIT);
-
 		/* Initialize kthread work structs */
 		kthread_init_work(&s->p[i].tx_work, sc16is7xx_tx_proc);
 		kthread_init_work(&s->p[i].reg_work, sc16is7xx_reg_proc);
@@ -1497,6 +1486,25 @@ static int sc16is7xx_probe(struct device *dev,
 					 prop, p, u)
 			if (u < devtype->nr_uart)
 				s->p[u].irda_mode = true;
+
+		val = 0;
+
+		of_property_for_each_u32(dev->of_node, "nxp,modem-control-line-ports",
+					 prop, p, u)
+			if (u < devtype->nr_uart) {
+				/* Use GPIO lines as modem control lines */
+				if (u == 0)
+					val |= SC16IS7XX_IOCONTROL_MODEM_A_BIT;
+				else if (u == 1)
+					val |= SC16IS7XX_IOCONTROL_MODEM_B_BIT;
+			}
+
+		if (val)
+			regmap_update_bits(
+				s->regmap,
+				SC16IS7XX_IOCONTROL_REG << SC16IS7XX_REG_SHIFT,
+				SC16IS7XX_IOCONTROL_MODEM_A_BIT |
+				SC16IS7XX_IOCONTROL_MODEM_B_BIT, val);
 	}
 
 #ifdef CONFIG_GPIOLIB
-- 
2.30.2