From a317449e0db1aad9fe15a47b3de47a3c647721e5 Mon Sep 17 00:00:00 2001
From: Sepherosa Ziehau <sephe@dragonflybsd.org>
Date: Mon, 16 Apr 2012 19:41:20 +0800
Subject: [PATCH] ifnet: Factor out if_ring_count2()

This function calculates maximum allowed power-of-2 ring count based on
user specified value (cnt) and the maximum number of rings supported by
the hardware (cnt_max).  The power-of-2 cpu count is also take into
consideration.
---
 sys/dev/netif/emx/if_emx.c |  8 +-------
 sys/dev/netif/jme/if_jme.c | 14 +++-----------
 sys/net/if.c               | 25 +++++++++++++++++++++++++
 sys/net/if_var.h           |  1 +
 4 files changed, 30 insertions(+), 18 deletions(-)

diff --git a/sys/dev/netif/emx/if_emx.c b/sys/dev/netif/emx/if_emx.c
index e5253395ea..526aa2a0de 100644
--- a/sys/dev/netif/emx/if_emx.c
+++ b/sys/dev/netif/emx/if_emx.c
@@ -533,13 +533,7 @@ emx_attach(device_t dev)
 
 	/* Calculate # of RX rings */
 	sc->rx_ring_cnt = device_getenv_int(dev, "rxr", emx_rxr);
-	if (sc->rx_ring_cnt <= 0 || sc->rx_ring_cnt > EMX_NRX_RING ||
-	    sc->rx_ring_cnt > ncpus) {
-		if (ncpus > 1)
-			sc->rx_ring_cnt = EMX_NRX_RING;
-		else
-			sc->rx_ring_cnt = 1;
-	}
+	sc->rx_ring_cnt = if_ring_count2(sc->rx_ring_cnt, EMX_NRX_RING);
 
 	/* Allocate RX/TX rings' busdma(9) stuffs */
 	error = emx_dma_alloc(sc);
diff --git a/sys/dev/netif/jme/if_jme.c b/sys/dev/netif/jme/if_jme.c
index d5b0f8f397..7554136369 100644
--- a/sys/dev/netif/jme/if_jme.c
+++ b/sys/dev/netif/jme/if_jme.c
@@ -653,18 +653,10 @@ jme_attach(device_t dev)
 		sc->jme_tx_desc_cnt = JME_NDESC_MAX;
 
 	/*
-	 * Calculate rx rings based on ncpus2
+	 * Calculate rx rings
 	 */
-	sc->jme_rx_ring_cnt = jme_rx_ring_count;
-	if (sc->jme_rx_ring_cnt <= 0)
-		sc->jme_rx_ring_cnt = JME_NRXRING_1;
-	if (sc->jme_rx_ring_cnt > ncpus2)
-		sc->jme_rx_ring_cnt = ncpus2;
-
-	if (sc->jme_rx_ring_cnt >= JME_NRXRING_4)
-		sc->jme_rx_ring_cnt = JME_NRXRING_4;
-	else if (sc->jme_rx_ring_cnt >= JME_NRXRING_2)
-		sc->jme_rx_ring_cnt = JME_NRXRING_2;
+	sc->jme_rx_ring_cnt = if_ring_count2(jme_rx_ring_count,
+	    JME_NRXRING_MAX);
 	sc->jme_rx_ring_inuse = sc->jme_rx_ring_cnt;
 
 	i = 0;
diff --git a/sys/net/if.c b/sys/net/if.c
index ec8a8c4eb3..827e0b3877 100644
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -2751,3 +2751,28 @@ if_deregister_com_alloc(u_char type)
         if_com_alloc[type] = NULL;
         if_com_free[type] = NULL;
 }
+
+int
+if_ring_count2(int cnt, int cnt_max)
+{
+	int shift = 0;
+
+	KASSERT(cnt_max >= 1 && powerof2(cnt_max),
+	    ("invalid ring count max %d\n", cnt_max));
+
+	if (cnt <= 0)
+		cnt = cnt_max;
+	if (cnt > ncpus2)
+		cnt = ncpus2;
+	if (cnt > cnt_max)
+		cnt = cnt_max;
+
+	while ((1 << (shift + 1)) <= cnt)
+		++shift;
+	cnt = 1 << shift;
+
+	KASSERT(cnt >= 1 && cnt <= ncpus2 && cnt <= cnt_max,
+	    ("calculate cnt %d, ncpus2 %d, cnt max %d\n",
+	     cnt, ncpus2, cnt_max));
+	return cnt;
+}
diff --git a/sys/net/if_var.h b/sys/net/if_var.h
index db37914303..4b352bf046 100644
--- a/sys/net/if_var.h
+++ b/sys/net/if_var.h
@@ -795,6 +795,7 @@ struct ifaddr *ifaddr_byindex(unsigned short);
 struct	ifmultiaddr *ifmaof_ifpforaddr(struct sockaddr *, struct ifnet *);
 int	if_simloop(struct ifnet *ifp, struct mbuf *m, int af, int hlen);
 void	if_devstart(struct ifnet *ifp);
+int	if_ring_count2(int cnt, int cnt_max);
 
 #define IF_LLSOCKADDR(ifp)						\
     ((struct sockaddr_dl *)(ifp)->if_lladdr->ifa_addr)
-- 
2.41.0