Input: psmouse - set up dependency between PS/2 and SMBus companions

When we switch from emulated PS/2 to native (RMI4 or Elan) protocols, we
create SMBus companion devices that are attached to I2C/SMBus controllers.
However, when suspending and resuming, we also need to make sure that we
take into account the PS/2 device they are associated with, so that PS/2
device is suspended after the companion and resumed before it, otherwise
companions will not work properly. Before I2C devices were marked for
asynchronous suspend/resume, this ordering happened naturally, but now we
need to enforce it by establishing device links, with PS/2 devices being
suppliers and SMBus companions being consumers.

Fixes: 172d931910e1 ("i2c: enable async suspend/resume on i2c client devices")
Reported-and-tested-by: Hugh Dickins <[e-mail]>
Tested-by: Jarkko Nikula <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/mouse/psmouse-smbus.c

···
 				    "Marking SMBus companion %s as gone\n",
 				    dev_name(&smbdev->client->dev));
 			smbdev->dead = true;
+			device_link_remove(&smbdev->client->dev,
+					   &smbdev->psmouse->ps2dev.serio->dev);
 			serio_rescan(smbdev->psmouse->ps2dev.serio);
 		} else {
 			list_del(&smbdev->node);
···
 		kfree(smbdev);
 	} else {
 		smbdev->dead = true;
+		device_link_remove(&smbdev->client->dev,
+				   &psmouse->ps2dev.serio->dev);
 		psmouse_dbg(smbdev->psmouse,
 			    "posting removal request for SMBus companion %s\n",
 			    dev_name(&smbdev->client->dev));
···
 
 	if (smbdev->client) {
 		/* We have our companion device */
+		if (!device_link_add(&smbdev->client->dev,
+				     &psmouse->ps2dev.serio->dev,
+				     DL_FLAG_STATELESS))
+			psmouse_warn(psmouse,
+				     "failed to set up link with iSMBus companion %s\n",
+				     dev_name(&smbdev->client->dev));
 		return 0;
 	}