On Sun, Aug 14, 2016 at 10:48:22AM +0200, Pavel Machek wrote:

On Sat 2016-08-13 12:03:45, Greg Kroah-Hartman wrote:

quoted

On Sat, Aug 13, 2016 at 05:14:33AM +0200, Sebastian Reichel wrote:

quoted

From: NeilBrown <redacted>

A "tty slave" is a device connected via UART.  It may need a driver to,
for example, power the device on when the tty is opened, and power it
off when the tty is released.

Signed-off-by: NeilBrown <redacted>
Signed-off-by: Sebastian Reichel <sre@kernel.org>

Acked-by: Pavel Machek <redacted>

quoted

quoted

@@ -3317,6 +3318,11 @@ struct device *tty_register_device_attr(struct tty_driver *driver,
 	retval = device_register(dev);
 	if (retval)
 		goto error;
+	if (device && device->of_node)
+		/* Children are platform devices and will be
+		 * runtime_pm managed by this tty.
+		 */
+		of_platform_populate(device->of_node, NULL, NULL, dev);

Why are these platform devices?  And why only OF?

OF based systems are the only ones that have this problem, so that's
the only place where we can test this solution.

Given that these devices are connected over the UART, it seems right
to categorize them as platform devices... You can't connect PCI, SATA
or USB device over UART port.

No, that's a total abuse of the platform bus, please don't.

I've said before that a "serial" bus should be created and you can hang
devices off of it.  For some reason that message keeps getting
ignored...

thanks,

greg k-h