w1-gpio: add external pull-up enable callback

On embedded devices, sleep mode conditions can be tricky to handle,
Especially when processors tend to pull-down the w1 bus during sleep. Bus
slaves (such as the ds2760) may interpret this as a reason for power-down
conditions and entirely switch off the device.

This patch adds a callback function pointer to let users switch on and off
the external pull-up resistor. This lets the outside world know whether
the processor is currently actively driving the bus or not.

When this callback is not provided, the code behaviour won't change.

Signed-off-by: Daniel Mack <[e-mail]>
Acked-by: Ville Syrjala <[e-mail]>
Acked-by: Evgeniy Polyakov <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/w1/masters/w1-gpio.c

···
 	if (err)
 		goto free_gpio;
 
+	if (pdata->enable_external_pullup)
+		pdata->enable_external_pullup(1);
+
 	platform_set_drvdata(pdev, master);
 
 	return 0;
···
 	struct w1_bus_master *master = platform_get_drvdata(pdev);
 	struct w1_gpio_platform_data *pdata = pdev->dev.platform_data;
 
+	if (pdata->enable_external_pullup)
+		pdata->enable_external_pullup(0);
+
 	w1_remove_master_device(master);
 	gpio_free(pdata->pin);
 	kfree(master);
···
 	return 0;
 }
 
+#ifdef CONFIG_PM
+
+static int w1_gpio_suspend(struct platform_device *pdev, pm_message_t state)
+{
+	struct w1_gpio_platform_data *pdata = pdev->dev.platform_data;
+
+	if (pdata->enable_external_pullup)
+		pdata->enable_external_pullup(0);
+
+	return 0;
+}
+
+static int w1_gpio_resume(struct platform_device *pdev)
+{
+	struct w1_gpio_platform_data *pdata = pdev->dev.platform_data;
+
+	if (pdata->enable_external_pullup)
+		pdata->enable_external_pullup(1);
+
+	return 0;
+}
+
+#else
+#define w1_gpio_suspend	NULL
+#define w1_gpio_resume	NULL
+#endif
+
 static struct platform_driver w1_gpio_driver = {
 	.driver = {
 		.name	= "w1-gpio",
 		.owner	= THIS_MODULE,
 	},
 	.remove	= __exit_p(w1_gpio_remove),
+	.suspend = w1_gpio_suspend,
+	.resume = w1_gpio_resume,
 };
 
 static int __init w1_gpio_init(void)

include/linux/w1-gpio.h

···
 struct w1_gpio_platform_data {
 	unsigned int pin;
 	unsigned int is_open_drain:1;
+	void (*enable_external_pullup)(int enable);
 };
 
 #endif /* _LINUX_W1_GPIO_H */