net: cdc_ncm: fix 64bit division build error

The upper timer_interval limit is arbitrary and much higher
than anything usable in the real world.  Reducing it from 15s
to ~4s to make the timer_interval fit in an u32 does not make
much difference.  The limit is still outside the practical
bounds.

This eliminates the need for a 64bit timer_interval, fixing a
build error related to 64bit division:

 drivers/built-in.o: In function `cdc_ncm_get_coalesce':
 ak8975.c:(.text+0x1ac994): undefined reference to `__aeabi_uldivmod'
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/cdc_ncm.c

@@ -138,7 +138,7 @@ static int cdc_ncm_get_coalesce(struct net_device *netdev,
 	ec->tx_max_coalesced_frames = ctx->tx_max / ctx->max_datagram_size;
 
 	/* the timer will fire CDC_NCM_TIMER_PENDING_CNT times in a row */
-	ec->tx_coalesce_usecs = (ctx->timer_interval * CDC_NCM_TIMER_PENDING_CNT) / NSEC_PER_USEC;
+	ec->tx_coalesce_usecs = ctx->timer_interval / (NSEC_PER_USEC / CDC_NCM_TIMER_PENDING_CNT);
 	return 0;
 }
 
@@ -164,7 +164,7 @@ static int cdc_ncm_set_coalesce(struct net_device *netdev,
 		return -EINVAL;
 
 	spin_lock_bh(&ctx->mtx);
-	ctx->timer_interval = ec->tx_coalesce_usecs * NSEC_PER_USEC / CDC_NCM_TIMER_PENDING_CNT;
+	ctx->timer_interval = ec->tx_coalesce_usecs * (NSEC_PER_USEC / CDC_NCM_TIMER_PENDING_CNT);
 	if (!ctx->timer_interval)
 		ctx->tx_timer_pending = 0;
 	spin_unlock_bh(&ctx->mtx);

include/linux/usb/cdc_ncm.h

@@ -78,7 +78,7 @@
 #define	CDC_NCM_TIMER_PENDING_CNT		2
 #define CDC_NCM_TIMER_INTERVAL_USEC		400UL
 #define CDC_NCM_TIMER_INTERVAL_MIN		5UL
-#define CDC_NCM_TIMER_INTERVAL_MAX		(15UL * USEC_PER_SEC)
+#define CDC_NCM_TIMER_INTERVAL_MAX		(U32_MAX / NSEC_PER_USEC)
 
 #define cdc_ncm_comm_intf_is_mbim(x)  ((x)->desc.bInterfaceSubClass == USB_CDC_SUBCLASS_MBIM && \
 				       (x)->desc.bInterfaceProtocol == USB_CDC_PROTO_NONE)
@@ -104,7 +104,7 @@ struct cdc_ncm_ctx {
 	spinlock_t mtx;
 	atomic_t stop;
 
-	u64 timer_interval;
+	u32 timer_interval;
 	u32 max_ndp_size;
 
 	u32 tx_timer_pending;