net: bcmgenet: test RBUF_ACPI_EN when resuming

When the GENET driver resumes from deep sleep the UMAC_CMD
register may not be accessible and therefore should not be
accessed from bcmgenet_wol_power_up_cfg() if the GENET has
been reset.

This commit adds a check of the RBUF_ACPI_EN flag when Wake
on Filter is enabled. A clear flag indicates that the GENET
hardware must have been reset so the remainder of the
hardware programming is bypassed.

Fixes: f50932cc ("net: bcmgenet: add WAKE_FILTER support")
Signed-off-by: Doug Berger <opendmb@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/genet/bcmgenet_wol.c

@@ -229,9 +229,13 @@ void bcmgenet_wol_power_up_cfg(struct bcmgenet_priv *priv,
 	}
 
 	/* Disable WAKE_FILTER Detection */
-	reg = bcmgenet_hfb_reg_readl(priv, HFB_CTRL);
-	reg &= ~(RBUF_HFB_EN | RBUF_ACPI_EN);
-	bcmgenet_hfb_reg_writel(priv, reg, HFB_CTRL);
+	if (priv->wolopts & WAKE_FILTER) {
+		reg = bcmgenet_hfb_reg_readl(priv, HFB_CTRL);
+		if (!(reg & RBUF_ACPI_EN))
+			return;	/* already reset so skip the rest */
+		reg &= ~(RBUF_HFB_EN | RBUF_ACPI_EN);
+		bcmgenet_hfb_reg_writel(priv, reg, HFB_CTRL);
+	}
 
 	/* Disable CRC Forward */
 	reg = bcmgenet_umac_readl(priv, UMAC_CMD);