drivers: net: xgene: Workaround for HW errata 10GE_4

This patch adds workaround for HW errata 10GE_4:
"XGENET_ICM_ECM_DROP_COUNT_REG_0 reg not clear on read".
Signed-off-by: Quan Nguyen <qnguyen@apm.com>
Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/apm/xgene/xgene_enet_hw.c

@@ -626,6 +626,8 @@ static void xgene_gmac_get_drop_cnt(struct xgene_enet_pdata *pdata,
 	xgene_enet_rd_mcx_csr(pdata, ICM_ECM_DROP_COUNT_REG0_ADDR, &count);
 	*rx = ICM_DROP_COUNT(count);
 	*tx = ECM_DROP_COUNT(count);
+	/* Errata: 10GE_4 - Fix ICM_ECM_DROP_COUNT not clear-on-read */
+	xgene_enet_rd_mcx_csr(pdata, ECM_CONFIG0_REG_0_ADDR, &count);
 }
 
 static void xgene_enet_config_ring_if_assoc(struct xgene_enet_pdata *pdata)

drivers/net/ethernet/apm/xgene/xgene_enet_sgmac.c

@@ -106,6 +106,11 @@ static void xgene_sgmac_get_drop_cnt(struct xgene_enet_pdata *pdata,
 	count = xgene_enet_rd_mcx_csr(pdata, addr);
 	*rx = ICM_DROP_COUNT(count);
 	*tx = ECM_DROP_COUNT(count);
+	/* Errata: 10GE_4 - ICM_ECM_DROP_COUNT not clear-on-read */
+	addr = (pdata->enet_id != XGENE_ENET1) ?
+		XG_MCX_ECM_CONFIG0_REG_0_ADDR :
+		ECM_CONFIG0_REG_0_ADDR + pdata->port_id * OFFSET_4;
+	xgene_enet_rd_mcx_csr(pdata, addr);
 }
 
 static void xgene_enet_config_ring_if_assoc(struct xgene_enet_pdata *p)

drivers/net/ethernet/apm/xgene/xgene_enet_xgmac.c

@@ -188,6 +188,8 @@ static void xgene_xgmac_get_drop_cnt(struct xgene_enet_pdata *pdata,
 	xgene_enet_rd_axg_csr(pdata, XGENET_ICM_ECM_DROP_COUNT_REG0, &count);
 	*rx = ICM_DROP_COUNT(count);
 	*tx = ECM_DROP_COUNT(count);
+	/* Errata: 10GE_4 - ICM_ECM_DROP_COUNT not clear-on-read */
+	xgene_enet_rd_axg_csr(pdata, XGENET_ECM_CONFIG0_REG_0, &count);
 }
 
 static void xgene_enet_config_ring_if_assoc(struct xgene_enet_pdata *pdata)