[PATCH net-next v2] net: stmmac: qcom-ethqos: remove MAC_CTRL_REG modification

["Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>]

When operating in "SGMII" mode (Cisco SGMII or 2500BASE-X), qcom-ethqos
modifies the MAC control register in its ethqos_configure_sgmii()
function, which is only called from one path:

stmmac_mac_link_up()
+- reads MAC_CTRL_REG
+- masks out priv->hw->link.speed_mask
+- sets bits according to speed (2500, 1000, 100, 10) from priv->hw.link.speed*
+- ethqos_fix_mac_speed()
|  +- qcom_ethqos_set_sgmii_loopback(false)
|  +- ethqos_update_link_clk(speed)
|  `- ethqos_configure(speed)
|     `- ethqos_configure_sgmii(speed)
|        +- reads MAC_CTRL_REG,
|        +- configures PS/FES bits according to speed
|        `- writes MAC_CTRL_REG as the last operation
+- sets duplex bit(s)
+- stmmac_mac_flow_ctrl()
+- writes MAC_CTRL_REG if changed from original read
...

As can be seen, the modification of the control register that
stmmac_mac_link_up() overwrites the changes that ethqos_fix_mac_speed()
does to the register. This makes ethqos_configure_sgmii()'s
modification questionable at best.

Analysing the values written, GMAC4 sets the speed bits as:
speed_mask = GMAC_CONFIG_FES | GMAC_CONFIG_PS
speed2500 = GMAC_CONFIG_FES                     B14=1 B15=0
speed1000 = 0                                   B14=0 B15=0
speed100 = GMAC_CONFIG_FES | GMAC_CONFIG_PS     B14=1 B15=1
speed10 = GMAC_CONFIG_PS                        B14=0 B15=1

Whereas ethqos_configure_sgmii():
2500: clears ETHQOS_MAC_CTRL_PORT_SEL           B14=X B15=0
1000: clears ETHQOS_MAC_CTRL_PORT_SEL           B14=X B15=0
100: sets ETHQOS_MAC_CTRL_PORT_SEL |            B14=1 B15=1
          ETHQOS_MAC_CTRL_SPEED_MODE
10: sets ETHQOS_MAC_CTRL_PORT_SEL               B14=0 B15=1
    clears ETHQOS_MAC_CTRL_SPEED_MODE

Thus, they appear to be doing very similar, with the exception of the
FES bit (bit 14) for 1G and 2.5G speeds.

Given that stmmac_mac_link_up() will write the MAC_CTRL_REG after
ethqos_configure_sgmii(), remove the unnecessary update in the
glue driver's ethqos_configure_sgmii() method, simplifying the code.

Konrad states:

Without any additional knowledge, the register description says:

2500: B14=1 B15=0
1000: B14=0 B15=0
 100: B14=1 B15=1
  10: B14=0 B15=1

Tested-by: Mohd Ayaan Anwar <mohd.anwar@oss.qualcomm.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---
v2: added tested-by/reviewed-by, added additional comments from Konrad
w.r.t. the register description to commit description (which is the
reason for resending.)

 .../ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c  | 16 +---------------
 1 file changed, 1 insertion(+), 15 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
index d1e48b524d7a..1a616a71c36a 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
@@ -76,10 +76,6 @@
 #define RGMII_CONFIG2_DATA_DIVIDE_CLK_SEL	BIT(6)
 #define RGMII_CONFIG2_TX_CLK_PHASE_SHIFT_EN	BIT(5)
 
-/* MAC_CTRL_REG bits */
-#define ETHQOS_MAC_CTRL_SPEED_MODE		BIT(14)
-#define ETHQOS_MAC_CTRL_PORT_SEL		BIT(15)
-
 /* EMAC_WRAPPER_SGMII_PHY_CNTRL1 bits */
 #define SGMII_PHY_CNTRL1_SGMII_TX_TO_RX_LOOPBACK_EN	BIT(3)
 
@@ -632,13 +628,9 @@ static int ethqos_configure_sgmii(struct qcom_ethqos *ethqos, int speed)
 {
 	struct net_device *dev = platform_get_drvdata(ethqos->pdev);
 	struct stmmac_priv *priv = netdev_priv(dev);
-	int val;
-
-	val = readl(ethqos->mac_base + MAC_CTRL_REG);
 
 	switch (speed) {
 	case SPEED_2500:
-		val &= ~ETHQOS_MAC_CTRL_PORT_SEL;
 		rgmii_updatel(ethqos, RGMII_CONFIG2_RGMII_CLK_SEL_CFG,
 			      RGMII_CONFIG2_RGMII_CLK_SEL_CFG,
 			      RGMII_IO_MACRO_CONFIG2);
@@ -646,7 +638,6 @@ static int ethqos_configure_sgmii(struct qcom_ethqos *ethqos, int speed)
 		ethqos_pcs_set_inband(priv, false);
 		break;
 	case SPEED_1000:
-		val &= ~ETHQOS_MAC_CTRL_PORT_SEL;
 		rgmii_updatel(ethqos, RGMII_CONFIG2_RGMII_CLK_SEL_CFG,
 			      RGMII_CONFIG2_RGMII_CLK_SEL_CFG,
 			      RGMII_IO_MACRO_CONFIG2);
@@ -654,13 +645,10 @@ static int ethqos_configure_sgmii(struct qcom_ethqos *ethqos, int speed)
 		ethqos_pcs_set_inband(priv, true);
 		break;
 	case SPEED_100:
-		val |= ETHQOS_MAC_CTRL_PORT_SEL | ETHQOS_MAC_CTRL_SPEED_MODE;
 		ethqos_set_serdes_speed(ethqos, SPEED_1000);
 		ethqos_pcs_set_inband(priv, true);
 		break;
 	case SPEED_10:
-		val |= ETHQOS_MAC_CTRL_PORT_SEL;
-		val &= ~ETHQOS_MAC_CTRL_SPEED_MODE;
 		rgmii_updatel(ethqos, RGMII_CONFIG_SGMII_CLK_DVDR,
 			      FIELD_PREP(RGMII_CONFIG_SGMII_CLK_DVDR,
 					 SGMII_10M_RX_CLK_DVDR),
@@ -670,9 +658,7 @@ static int ethqos_configure_sgmii(struct qcom_ethqos *ethqos, int speed)
 		break;
 	}
 
-	writel(val, ethqos->mac_base + MAC_CTRL_REG);
-
-	return val;
+	return 0;
 }
 
 static int ethqos_configure(struct qcom_ethqos *ethqos, int speed)
-- 
2.47.3