[PATCH] OMAP/serial: Add support for driving a GPIO as DTR.

[NeilBrown]

Hi all,
 this is my current patch which answers my question from May:
     Question:  How to power-manage UART-attached devices.

 It teaches omap2/serial about the possibility of a GPIO which is to be
 driven as a DTR line. 
 This allows me to power on/off devices that are accessed via a serial port
 (GPS, Bluetooth) when the port is opened/closed.  I simply write a driver
 which exports a GPIO line and does the required magic when it is driven
 high or low.

 - because '0' is a valid GPIO number, I added an extra port_info field
   call 'DTR_present' so existing code wouldn't accidentally request to
   use GPIO-0 as a DTR - is there a better way to handle this?
 - I added a DTR_inverted field so you could choose the polarity of the
   GPIO line ... I'm not really sure this is needed so I'll probably drop it
   unless encouraged otherwise.

 - If the gpio 'can_sleep', then I need a work-queue to effect the change, and
   I currently use the 'qos_work' rather than adding another work handler.
   As both the qos_work and the gpio work tasks are idempotent and rare, this
   seems reasonable.  Is it OK?  should I make another work_struct? or
   something else?

Thanks,
NeilBrown




---------------------
OMAP hardware doesn't provide a phyisical DTR line, but
some configurations may need a DTR line which tracks whether
the device is open or not.

So allow a gpio to be configured as the DTR line.

Signed-off-by: NeilBrown <neilb@xxxxxxx>

diff --git a/arch/arm/mach-omap2/serial.c b/arch/arm/mach-omap2/serial.c
index c1b93c7..25d53b2 100644
--- a/arch/arm/mach-omap2/serial.c
+++ b/arch/arm/mach-omap2/serial.c
@@ -304,6 +304,9 @@ void __init omap_serial_init_port(struct omap_board_data *bdata,
 	omap_up.dma_rx_timeout = info->dma_rx_timeout;
 	omap_up.dma_rx_poll_rate = info->dma_rx_poll_rate;
 	omap_up.autosuspend_timeout = info->autosuspend_timeout;
+	omap_up.DTR_gpio = info->DTR_gpio;
+	omap_up.DTR_inverted = info->DTR_inverted;
+	omap_up.DTR_present = info->DTR_present;
 
 	pdata = &omap_up;
 	pdata_size = sizeof(struct omap_uart_port_info);
diff --git a/arch/arm/plat-omap/include/plat/omap-serial.h b/arch/arm/plat-omap/include/plat/omap-serial.h
index 1a52725..52d3de4 100644
--- a/arch/arm/plat-omap/include/plat/omap-serial.h
+++ b/arch/arm/plat-omap/include/plat/omap-serial.h
@@ -69,6 +69,9 @@ struct omap_uart_port_info {
 	unsigned int		dma_rx_timeout;
 	unsigned int		autosuspend_timeout;
 	unsigned int		dma_rx_poll_rate;
+	int			DTR_gpio;
+	int			DTR_inverted;
+	int			DTR_present;
 
 	int (*get_context_loss_count)(struct device *);
 	void (*set_forceidle)(struct platform_device *);
@@ -131,6 +134,10 @@ struct uart_omap_port {
 	u32			errata;
 	u8			wakeups_enabled;
 
+	int			DTR_gpio;
+	int			DTR_inverted;
+	int			DTR_active;
+
 	struct pm_qos_request	pm_qos_request;
 	u32			latency;
 	u32			calc_latency;
diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index d3cda0c..aa603f2 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -39,6 +39,7 @@
 #include <linux/irq.h>
 #include <linux/pm_runtime.h>
 #include <linux/of.h>
+#include <linux/gpio.h>
 
 #include <plat/dma.h>
 #include <plat/dmtimer.h>
@@ -507,6 +508,16 @@ static void serial_omap_set_mctrl(struct uart_port *port, unsigned int mctrl)
 	up->mcr |= mcr;
 	serial_out(up, UART_MCR, up->mcr);
 	pm_runtime_put(&up->pdev->dev);
+
+	if (gpio_is_valid(up->DTR_gpio) &&
+	    !!(mctrl & TIOCM_DTR) != up->DTR_active) {
+		up->DTR_active = !up->DTR_active;
+		if (gpio_cansleep(up->DTR_gpio))
+			schedule_work(&up->qos_work);
+		else
+			gpio_set_value(up->DTR_gpio,
+				       up->DTR_active != up->DTR_inverted);
+	}
 }
 
 static void serial_omap_break_ctl(struct uart_port *port, int break_state)
@@ -715,6 +726,9 @@ static void serial_omap_uart_qos_work(struct work_struct *work)
 						qos_work);
 
 	pm_qos_update_request(&up->pm_qos_request, up->latency);
+	if (gpio_is_valid(up->DTR_gpio))
+		gpio_set_value_cansleep(up->DTR_gpio,
+					up->DTR_active != up->DTR_inverted);
 }
 
 static void
@@ -1435,7 +1449,7 @@ static int serial_omap_probe(struct platform_device *pdev)
 	struct uart_omap_port	*up;
 	struct resource		*mem, *irq, *dma_tx, *dma_rx;
 	struct omap_uart_port_info *omap_up_info = pdev->dev.platform_data;
-	int ret = -ENOSPC;
+	int ret;
 
 	if (pdev->dev.of_node)
 		omap_up_info = of_get_uart_port_info(&pdev->dev);
@@ -1466,10 +1480,29 @@ static int serial_omap_probe(struct platform_device *pdev)
 	if (!dma_tx)
 		return -ENXIO;
 
+	if (gpio_is_valid(omap_up_info->DTR_gpio) &&
+	    omap_up_info->DTR_present) {
+		ret = gpio_request(omap_up_info->DTR_gpio, "omap-serial");
+		if (ret < 0)
+			return ret;
+		ret = gpio_direction_output(omap_up_info->DTR_gpio,
+					    omap_up_info->DTR_inverted);
+		if (ret < 0)
+			return ret;
+	}
+
 	up = devm_kzalloc(&pdev->dev, sizeof(*up), GFP_KERNEL);
 	if (!up)
 		return -ENOMEM;
 
+	if (gpio_is_valid(omap_up_info->DTR_gpio) &&
+	    omap_up_info->DTR_present) {
+		up->DTR_gpio = omap_up_info->DTR_gpio;
+		up->DTR_inverted = omap_up_info->DTR_inverted;
+	} else
+		up->DTR_gpio = -EINVAL;
+	up->DTR_active = 0;
+
 	up->pdev = pdev;
 	up->port.dev = &pdev->dev;
 	up->port.type = PORT_OMAP;

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