stmmac: dwmac-mediatek: remove the dwmac_fix_mac_speed

In current driver, MAC will always enable 2ns delay in RGMII mode,
but that's not the correct usage.

Remove the dwmac_fix_mac_speed() in driver, and recommend "rgmii-id"
for phy-mode in device tree.

Fixes: f2d356a ("stmmac: dwmac-mediatek: add support for mt8195")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Biao Huang <biao.huang@mediatek.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/stmicro/stmmac/dwmac-mediatek.c

@@ -90,7 +90,6 @@ struct mediatek_dwmac_plat_data {
 struct mediatek_dwmac_variant {
 	int (*dwmac_set_phy_interface)(struct mediatek_dwmac_plat_data *plat);
 	int (*dwmac_set_delay)(struct mediatek_dwmac_plat_data *plat);
-	void (*dwmac_fix_mac_speed)(void *priv, unsigned int speed);
 
 	/* clock ids to be requested */
 	const char * const *clk_list;
@@ -443,32 +442,9 @@ static int mt8195_set_delay(struct mediatek_dwmac_plat_data *plat)
 	return 0;
 }
 
-static void mt8195_fix_mac_speed(void *priv, unsigned int speed)
-{
-	struct mediatek_dwmac_plat_data *priv_plat = priv;
-
-	if ((phy_interface_mode_is_rgmii(priv_plat->phy_mode))) {
-		/* prefer 2ns fixed delay which is controlled by TXC_PHASE_CTRL,
-		 * when link speed is 1Gbps with RGMII interface,
-		 * Fall back to delay macro circuit for 10/100Mbps link speed.
-		 */
-		if (speed == SPEED_1000)
-			regmap_update_bits(priv_plat->peri_regmap,
-					   MT8195_PERI_ETH_CTRL0,
-					   MT8195_RGMII_TXC_PHASE_CTRL |
-					   MT8195_DLY_GTXC_ENABLE |
-					   MT8195_DLY_GTXC_INV |
-					   MT8195_DLY_GTXC_STAGES,
-					   MT8195_RGMII_TXC_PHASE_CTRL);
-		else
-			mt8195_set_delay(priv_plat);
-	}
-}
-
 static const struct mediatek_dwmac_variant mt8195_gmac_variant = {
 	.dwmac_set_phy_interface = mt8195_set_interface,
 	.dwmac_set_delay = mt8195_set_delay,
-	.dwmac_fix_mac_speed = mt8195_fix_mac_speed,
 	.clk_list = mt8195_dwmac_clk_l,
 	.num_clks = ARRAY_SIZE(mt8195_dwmac_clk_l),
 	.dma_bit_mask = 35,
@@ -619,8 +595,6 @@ static int mediatek_dwmac_common_data(struct platform_device *pdev,
 	plat->bsp_priv = priv_plat;
 	plat->init = mediatek_dwmac_init;
 	plat->clks_config = mediatek_dwmac_clks_config;
-	if (priv_plat->variant->dwmac_fix_mac_speed)
-		plat->fix_mac_speed = priv_plat->variant->dwmac_fix_mac_speed;
 
 	plat->safety_feat_cfg = devm_kzalloc(&pdev->dev,
 					     sizeof(*plat->safety_feat_cfg),