drivers/w1/masters/w1-gpio.c: add strong pullup emulation

Strong pullup is emulated by driving pin logic high after write command
when using tri-state push-pull GPIO.

Signed-off-by: Evgeny Boger <boger@contactless.ru>
Cc: Greg KH <greg@kroah.com>
Acked-by: David Fries <david@fries.net>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/w1/masters/w1-gpio.c

@@ -18,10 +18,31 @@
 #include <linux/of_gpio.h>
 #include <linux/err.h>
 #include <linux/of.h>
+#include <linux/delay.h>
 
 #include "../w1.h"
 #include "../w1_int.h"
 
+static u8 w1_gpio_set_pullup(void *data, int delay)
+{
+	struct w1_gpio_platform_data *pdata = data;
+
+	if (delay) {
+		pdata->pullup_duration = delay;
+	} else {
+		if (pdata->pullup_duration) {
+			gpio_direction_output(pdata->pin, 1);
+
+			msleep(pdata->pullup_duration);
+
+			gpio_direction_input(pdata->pin);
+		}
+		pdata->pullup_duration = 0;
+	}
+
+	return 0;
+}
+
 static void w1_gpio_write_bit_dir(void *data, u8 bit)
 {
 	struct w1_gpio_platform_data *pdata = data;
@@ -132,6 +153,7 @@ static int w1_gpio_probe(struct platform_device *pdev)
 	} else {
 		gpio_direction_input(pdata->pin);
 		master->write_bit = w1_gpio_write_bit_dir;
+		master->set_pullup = w1_gpio_set_pullup;
 	}
 
 	err = w1_add_master_device(master);

drivers/w1/w1_int.c

@@ -117,18 +117,6 @@ int w1_add_master_device(struct w1_bus_master *master)
 		printk(KERN_ERR "w1_add_master_device: invalid function set\n");
 		return(-EINVAL);
         }
-	/* While it would be electrically possible to make a device that
-	 * generated a strong pullup in bit bang mode, only hardware that
-	 * controls 1-wire time frames are even expected to support a strong
-	 * pullup.  w1_io.c would need to support calling set_pullup before
-	 * the last write_bit operation of a w1_write_8 which it currently
-	 * doesn't.
-	 */
-	if (!master->write_byte && !master->touch_bit && master->set_pullup) {
-		printk(KERN_ERR "w1_add_master_device: set_pullup requires "
-			"write_byte or touch_bit, disabling\n");
-		master->set_pullup = NULL;
-	}
 
 	/* Lock until the device is added (or not) to w1_masters. */
 	mutex_lock(&w1_mlock);

include/linux/w1-gpio.h

@@ -20,6 +20,7 @@ struct w1_gpio_platform_data {
 	unsigned int is_open_drain:1;
 	void (*enable_external_pullup)(int enable);
 	unsigned int ext_pullup_enable_pin;
+	unsigned int pullup_duration;
 };
 
 #endif /* _LINUX_W1_GPIO_H */