s390/lcs: Remove FDDI option

The last s390 machine that supported FDDI was z900 ('7th generation',
released in 2000). The oldest machine generation currently supported by
the Linux kernel is MARCH_Z10 (released 2008). If there is still a usecase
for connecting a Linux on s390 instance to a LAN Channel Station (LCS), it
can only do so via Ethernet.

Randy Dunlap[1] found that LCS over FDDI has never worked, when FDDI
was compiled as module. Instead of fixing that, remove the FDDI option
from the lcs driver.

While at it, make the CONFIG_LCS description a bit more helpful.

References:
[1] https://lore.kernel.org/netdev/20230621213742.8245-1-rdunlap@infradead.org/

Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230724131546.3597001-1-wintera@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/s390/net/Kconfig

@@ -5,12 +5,11 @@ menu "S/390 network device drivers"
 config LCS
 	def_tristate m
 	prompt "Lan Channel Station Interface"
-	depends on CCW && NETDEVICES && (ETHERNET || FDDI)
+	depends on CCW && NETDEVICES && ETHERNET
 	help
 	  Select this option if you want to use LCS networking on IBM System z.
-	  This device driver supports FDDI (IEEE 802.7) and Ethernet.
 	  To compile as a module, choose M. The module name is lcs.
-	  If you do not know what it is, it's safe to choose Y.
+	  If you do not use LCS, choose N.
 
 config CTCM
 	def_tristate m

drivers/s390/net/lcs.c

@@ -17,7 +17,6 @@
 #include <linux/if.h>
 #include <linux/netdevice.h>
 #include <linux/etherdevice.h>
-#include <linux/fddidevice.h>
 #include <linux/inetdevice.h>
 #include <linux/in.h>
 #include <linux/igmp.h>
@@ -36,10 +35,6 @@
 #include "lcs.h"
 
 
-#if !defined(CONFIG_ETHERNET) && !defined(CONFIG_FDDI)
-#error Cannot compile lcs.c without some net devices switched on.
-#endif
-
 /*
  * initialization string for output
  */
@@ -1601,19 +1596,11 @@ lcs_startlan_auto(struct lcs_card *card)
 	int rc;
 
 	LCS_DBF_TEXT(2, trace, "strtauto");
-#ifdef CONFIG_ETHERNET
 	card->lan_type = LCS_FRAME_TYPE_ENET;
 	rc = lcs_send_startlan(card, LCS_INITIATOR_TCPIP);
 	if (rc == 0)
 		return 0;
 
-#endif
-#ifdef CONFIG_FDDI
-	card->lan_type = LCS_FRAME_TYPE_FDDI;
-	rc = lcs_send_startlan(card, LCS_INITIATOR_TCPIP);
-	if (rc == 0)
-		return 0;
-#endif
 	return -EIO;
 }
 
@@ -1806,22 +1793,16 @@ lcs_get_frames_cb(struct lcs_channel *channel, struct lcs_buffer *buffer)
 			card->stats.rx_errors++;
 			return;
 		}
-		/* What kind of frame is it? */
-		if (lcs_hdr->type == LCS_FRAME_TYPE_CONTROL) {
-			/* Control frame. */
+		if (lcs_hdr->type == LCS_FRAME_TYPE_CONTROL)
 			lcs_get_control(card, (struct lcs_cmd *) lcs_hdr);
-		} else if (lcs_hdr->type == LCS_FRAME_TYPE_ENET ||
-			   lcs_hdr->type == LCS_FRAME_TYPE_TR ||
-			   lcs_hdr->type == LCS_FRAME_TYPE_FDDI) {
-			/* Normal network packet. */
+		else if (lcs_hdr->type == LCS_FRAME_TYPE_ENET)
 			lcs_get_skb(card, (char *)(lcs_hdr + 1),
 				    lcs_hdr->offset - offset -
 				    sizeof(struct lcs_header));
-		} else {
-			/* Unknown frame type. */
-			; // FIXME: error message ?
-		}
-		/* Proceed to next frame. */
+		else
+			dev_info_once(&card->dev->dev,
+				      "Unknown frame type %d\n",
+				      lcs_hdr->type);
 		offset = lcs_hdr->offset;
 		lcs_hdr->offset = LCS_ILLEGAL_OFFSET;
 		lcs_hdr = (struct lcs_header *) (buffer->data + offset);
@@ -2140,18 +2121,10 @@ lcs_new_device(struct ccwgroup_device *ccwgdev)
 		goto netdev_out;
 	}
 	switch (card->lan_type) {
-#ifdef CONFIG_ETHERNET
 	case LCS_FRAME_TYPE_ENET:
 		card->lan_type_trans = eth_type_trans;
 		dev = alloc_etherdev(0);
 		break;
-#endif
-#ifdef CONFIG_FDDI
-	case LCS_FRAME_TYPE_FDDI:
-		card->lan_type_trans = fddi_type_trans;
-		dev = alloc_fddidev(0);
-		break;
-#endif
 	default:
 		LCS_DBF_TEXT(3, setup, "errinit");
 		pr_err(" Initialization failed\n");