net: stmmac: selftest: avoid large stack usage

Putting a struct stmmac_rss object on the stack is a bad idea,
as it exceeds the warning limit for a stack frame on 32-bit architectures:

drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c:1221:12: error: stack frame size of 1208 bytes in function '__stmmac_test_l3filt' [-Werror,-Wframe-larger-than=]
drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c:1338:12: error: stack frame size of 1208 bytes in function '__stmmac_test_l4filt' [-Werror,-Wframe-larger-than=]

As the object is the trivial empty case, change the called function
to accept a NULL pointer to mean the same thing and remove the
large variable in the two callers.

Fixes: 4647e02 ("net: stmmac: selftests: Add selftest for L3/L4 Filters")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>

drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c

@@ -523,19 +523,18 @@ static int dwxgmac2_rss_configure(struct mac_device_info *hw,
 				  struct stmmac_rss *cfg, u32 num_rxq)
 {
 	void __iomem *ioaddr = hw->pcsr;
-	u32 *key = (u32 *)cfg->key;
 	int i, ret;
 	u32 value;
 
 	value = readl(ioaddr + XGMAC_RSS_CTRL);
-	if (!cfg->enable) {
+	if (!cfg || !cfg->enable) {
 		value &= ~XGMAC_RSSE;
 		writel(value, ioaddr + XGMAC_RSS_CTRL);
 		return 0;
 	}
 
 	for (i = 0; i < (sizeof(cfg->key) / sizeof(u32)); i++) {
-		ret = dwxgmac2_rss_write_reg(ioaddr, true, i, *key++);
+		ret = dwxgmac2_rss_write_reg(ioaddr, true, i, cfg->key[i]);
 		if (ret)
 			return ret;
 	}

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

@@ -1233,12 +1233,9 @@ static int __stmmac_test_l3filt(struct stmmac_priv *priv, u32 dst, u32 src,
 		return -EOPNOTSUPP;
 	if (!priv->dma_cap.l3l4fnum)
 		return -EOPNOTSUPP;
-	if (priv->rss.enable) {
-		struct stmmac_rss rss = { .enable = false, };
-
-		stmmac_rss_configure(priv, priv->hw, &rss,
+	if (priv->rss.enable)
+		stmmac_rss_configure(priv, priv->hw, NULL,
 				     priv->plat->rx_queues_to_use);
-	}
 
 	dissector = kzalloc(sizeof(*dissector), GFP_KERNEL);
 	if (!dissector) {
@@ -1357,12 +1354,9 @@ static int __stmmac_test_l4filt(struct stmmac_priv *priv, u32 dst, u32 src,
 		return -EOPNOTSUPP;
 	if (!priv->dma_cap.l3l4fnum)
 		return -EOPNOTSUPP;
-	if (priv->rss.enable) {
-		struct stmmac_rss rss = { .enable = false, };
-
-		stmmac_rss_configure(priv, priv->hw, &rss,
+	if (priv->rss.enable)
+		stmmac_rss_configure(priv, priv->hw, NULL,
 				     priv->plat->rx_queues_to_use);
-	}
 
 	dissector = kzalloc(sizeof(*dissector), GFP_KERNEL);
 	if (!dissector) {