net: stmmac: remove useless priv->flow_ctrl

priv->flow_ctrl is only accessed by stmmac_main.c, and the only place
that it is read is in stmmac_mac_flow_ctrl(). This function is only
called from stmmac_mac_link_up() which always sets priv->flow_ctrl
immediately before calling this function.

Therefore, initialising this at probe time is ineffectual because it
will always be overwritten before it's read. As such, the "flow_ctrl"
module parameter has been useless for some time. Rather than remove
the module parameter, which would risk module load failure, change the
description to indicate that it is obsolete, and warn if it is set by
userspace.

Moreover, storing the value in the stmmac_priv has no benefit as it's
set and then immediately read stmmac_mac_flow_ctrl(). Instead, pass it
as a parameter to this function..

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Link: https://patch.msgid.link/E1tkKmI-004ObG-DL@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/stmicro/stmmac/stmmac.h

@@ -282,7 +282,6 @@ struct stmmac_priv {
 	struct stmmac_channel channel[STMMAC_CH_MAX];
 
 	int speed;
-	unsigned int flow_ctrl;
 	unsigned int pause_time;
 	struct mii_bus *mii;
 

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -88,9 +88,9 @@ MODULE_PARM_DESC(phyaddr, "Physical device address");
 #define STMMAC_XDP_TX		BIT(1)
 #define STMMAC_XDP_REDIRECT	BIT(2)
 
-static int flow_ctrl = FLOW_AUTO;
+static int flow_ctrl = 0xdead;
 module_param(flow_ctrl, int, 0644);
-MODULE_PARM_DESC(flow_ctrl, "Flow control ability [on/off]");
+MODULE_PARM_DESC(flow_ctrl, "Flow control ability [on/off] (obsolete)");
 
 static int pause = PAUSE_TIME;
 module_param(pause, int, 0644);
@@ -188,12 +188,11 @@ static void stmmac_verify_args(void)
 		watchdog = TX_TIMEO;
 	if (unlikely((buf_sz < DEFAULT_BUFSIZE) || (buf_sz > BUF_SIZE_16KiB)))
 		buf_sz = DEFAULT_BUFSIZE;
-	if (unlikely(flow_ctrl > 1))
-		flow_ctrl = FLOW_AUTO;
-	else if (likely(flow_ctrl < 0))
-		flow_ctrl = FLOW_OFF;
 	if (unlikely((pause < 0) || (pause > 0xffff)))
 		pause = PAUSE_TIME;
+
+	if (flow_ctrl != 0xdead)
+		pr_warn("stmmac: module parameter 'flow_ctrl' is obsolete - please remove from your module configuration\n");
 }
 
 static void __stmmac_disable_all_queues(struct stmmac_priv *priv)
@@ -858,14 +857,16 @@ static void stmmac_release_ptp(struct stmmac_priv *priv)
  *  stmmac_mac_flow_ctrl - Configure flow control in all queues
  *  @priv: driver private structure
  *  @duplex: duplex passed to the next function
+ *  @flow_ctrl: desired flow control modes
  *  Description: It is used for configuring the flow control in all queues
  */
-static void stmmac_mac_flow_ctrl(struct stmmac_priv *priv, u32 duplex)
+static void stmmac_mac_flow_ctrl(struct stmmac_priv *priv, u32 duplex,
+				 unsigned int flow_ctrl)
 {
 	u32 tx_cnt = priv->plat->tx_queues_to_use;
 
-	stmmac_flow_ctrl(priv, priv->hw, duplex, priv->flow_ctrl,
-			 priv->pause_time, tx_cnt);
+	stmmac_flow_ctrl(priv, priv->hw, duplex, flow_ctrl, priv->pause_time,
+			 tx_cnt);
 }
 
 static unsigned long stmmac_mac_get_caps(struct phylink_config *config,
@@ -925,6 +926,7 @@ static void stmmac_mac_link_up(struct phylink_config *config,
 			       bool tx_pause, bool rx_pause)
 {
 	struct stmmac_priv *priv = netdev_priv(to_net_dev(config->dev));
+	unsigned int flow_ctrl;
 	u32 old_ctrl, ctrl;
 
 	if ((priv->plat->flags & STMMAC_FLAG_SERDES_UP_AFTER_PHY_LINKUP) &&
@@ -1005,15 +1007,15 @@ static void stmmac_mac_link_up(struct phylink_config *config,
 
 	/* Flow Control operation */
 	if (rx_pause && tx_pause)
-		priv->flow_ctrl = FLOW_AUTO;
+		flow_ctrl = FLOW_AUTO;
 	else if (rx_pause && !tx_pause)
-		priv->flow_ctrl = FLOW_RX;
+		flow_ctrl = FLOW_RX;
 	else if (!rx_pause && tx_pause)
-		priv->flow_ctrl = FLOW_TX;
+		flow_ctrl = FLOW_TX;
 	else
-		priv->flow_ctrl = FLOW_OFF;
+		flow_ctrl = FLOW_OFF;
 
-	stmmac_mac_flow_ctrl(priv, duplex);
+	stmmac_mac_flow_ctrl(priv, duplex, flow_ctrl);
 
 	if (ctrl != old_ctrl)
 		writel(ctrl, priv->ioaddr + MAC_CTRL_REG);
@@ -7600,9 +7602,6 @@ int stmmac_dvr_probe(struct device *device,
 			 "%s: warning: maxmtu having invalid value (%d)\n",
 			 __func__, priv->plat->maxmtu);
 
-	if (flow_ctrl)
-		priv->flow_ctrl = FLOW_AUTO;	/* RX/TX pause on */
-
 	ndev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
 
 	/* Setup channels NAPI */