[ISDN] capidrv: address two longstanding warnings

* change #warning to a code comment

* add comment and special ifdef'd 64-bit code for a situation where
  we must store a pointer into a CAPI field 'Data', which is fixed by
  the interface at 32 bits.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Acked-by: Karsten Keil <kkeil@suse.de>

drivers/isdn/capi/capidrv.c

@@ -1843,6 +1843,7 @@ static int if_sendbuf(int id, int channel, int doack, struct sk_buff *skb)
 	int msglen;
 	u16 errcode;
 	u16 datahandle;
+	u32 data;
 
 	if (!card) {
 		printk(KERN_ERR "capidrv: if_sendbuf called with invalid driverId %d!\n",
@@ -1860,9 +1861,26 @@ static int if_sendbuf(int id, int channel, int doack, struct sk_buff *skb)
 		return 0;
 	}
 	datahandle = nccip->datahandle;
+
+	/*
+	 * Here we copy pointer skb->data into the 32-bit 'Data' field.
+	 * The 'Data' field is not used in practice in linux kernel
+	 * (neither in 32 or 64 bit), but should have some value,
+	 * since a CAPI message trace will display it.
+	 *
+	 * The correct value in the 32 bit case is the address of the
+	 * data, in 64 bit it makes no sense, we use 0 there.
+	 */
+
+#ifdef CONFIG_64BIT
+	data = 0;
+#else
+	data = (unsigned long) skb->data;
+#endif
+
 	capi_fill_DATA_B3_REQ(&sendcmsg, global.ap.applid, card->msgid++,
 			      nccip->ncci,	/* adr */
-			      (u32) skb->data,	/* Data */
+			      data,		/* Data */
 			      skb->len,		/* DataLength */
 			      datahandle,	/* DataHandle */
 			      0	/* Flags */
@@ -2123,7 +2141,10 @@ static int capidrv_delcontr(u16 contr)
 		printk(KERN_ERR "capidrv: delcontr: no contr %u\n", contr);
 		return -1;
 	}
-	#warning FIXME: maybe a race condition the card should be removed here from global list /kkeil
+
+	/* FIXME: maybe a race condition the card should be removed
+	 * here from global list /kkeil
+	 */
 	spin_unlock_irqrestore(&global_lock, flags);
 
 	del_timer(&card->listentimer);