s390/qeth: phase out OSN support

OSN devices currently spend an awful long time in qeth_l2_set_online()
until various unsupported HW cmds time out. This has been broken for
over two years, ever since
commit d22ffb5a71 ("s390/qeth: fix IPA command submission race")
triggered a FW bug in cmd processing.
Prior to commit 782e4a7921 ("s390/qeth: don't poll for cmd IO completion"),
this wait for timeout would have even been spent busy-polling.

The offending patch was picked up by stable and all relevant distros,
and yet noone noticed.
OSN setups only ever worked in combination with an out-of-tree blob, and
the last machine that even offered HW with OSN support was released back
in 2015.

Rather than attempting to work-around this FW issue for no actual gain,
add a deprecation warning so anyone who still wants to maintain this
part of the code can speak up. Else rip it all out in 2021.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/s390/net/Kconfig

@@ -97,6 +97,7 @@ config QETH_OSN
 	depends on QETH
 	help
 	  This enables the qeth driver to support devices in OSN mode.
+	  This feature will be removed in 2021.
 	  If unsure, choose N.
 
 config QETH_OSX

drivers/s390/net/qeth_l2_main.c

@@ -587,6 +587,9 @@ static int qeth_l2_probe_device(struct ccwgroup_device *gdev)
 	struct qeth_card *card = dev_get_drvdata(&gdev->dev);
 	int rc;
 
+	if (IS_OSN(card))
+		dev_notice(&gdev->dev, "OSN support will be dropped in 2021\n");
+
 	qeth_l2_vnicc_set_defaults(card);
 	mutex_init(&card->sbp_lock);