net: dsa: mt7530: clean up core and TRGMII clock setup

Three minor changes:

- When disabling PLL, there is no need to call core_write_mmd_indirect
  directly, use the core_write wrapper instead like the rest of the code
  in the function does. This change helps with consistency and
  readability. Move the comment to the definition of
  core_read_mmd_indirect where it belongs.

- Disable both core and TRGMII Tx clocks prior to reconfiguring.
  Previously, only the core clock was disabled, but not TRGMII Tx clock.
  So disable both, then configure them, then re-enable both, for
  consistency.

- The core clock enable bit (REG_GSWCK_EN) is written redundantly three
  times. Simplify the code and only write the register only once at the
  end of clock reconfiguration to enable both core and TRGMII Tx clocks.

Tested on Ubiquiti ER-X running the GMAC0 and MT7530 in TRGMII mode.
Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mt7530.c

@@ -67,6 +67,11 @@ static const struct mt7530_mib_desc mt7530_mib[] = {
 	MIB_DESC(1, 0xb8, "RxArlDrop"),
 };
 
+/* Since phy_device has not yet been created and
+ * phy_{read,write}_mmd_indirect is not available, we provide our own
+ * core_{read,write}_mmd_indirect with core_{clear,write,set} wrappers
+ * to complete this function.
+ */
 static int
 core_read_mmd_indirect(struct mt7530_priv *priv, int prtad, int devad)
 {
@@ -435,19 +440,13 @@ mt7530_pad_clk_setup(struct dsa_switch *ds, phy_interface_t interface)
 		mt7530_write(priv, MT7530_TRGMII_TD_ODT(i),
 			     TD_DM_DRVP(8) | TD_DM_DRVN(8));
 
-	/* Setup core clock for MT7530 */
-	/* Disable MT7530 core clock */
-	core_clear(priv, CORE_TRGMII_GSW_CLK_CG, REG_GSWCK_EN);
+	/* Disable MT7530 core and TRGMII Tx clocks */
+	core_clear(priv, CORE_TRGMII_GSW_CLK_CG,
+		   REG_GSWCK_EN | REG_TRGMIICK_EN);
 
-	/* Disable PLL, since phy_device has not yet been created
-	 * provided for phy_[read,write]_mmd_indirect is called, we
-	 * provide our own core_write_mmd_indirect to complete this
-	 * function.
-	 */
-	core_write_mmd_indirect(priv,
-				CORE_GSWPLL_GRP1,
-				MDIO_MMD_VEND2,
-				0);
+	/* Setup core clock for MT7530 */
+	/* Disable PLL */
+	core_write(priv, CORE_GSWPLL_GRP1, 0);
 
 	/* Set core clock into 500Mhz */
 	core_write(priv, CORE_GSWPLL_GRP2,
@@ -460,11 +459,7 @@ mt7530_pad_clk_setup(struct dsa_switch *ds, phy_interface_t interface)
 		   RG_GSWPLL_POSDIV_200M(2) |
 		   RG_GSWPLL_FBKDIV_200M(32));
 
-	/* Enable MT7530 core clock */
-	core_set(priv, CORE_TRGMII_GSW_CLK_CG, REG_GSWCK_EN);
-
 	/* Setup the MT7530 TRGMII Tx Clock */
-	core_set(priv, CORE_TRGMII_GSW_CLK_CG, REG_GSWCK_EN);
 	core_write(priv, CORE_PLL_GROUP5, RG_LCDDS_PCW_NCPO1(ncpo1));
 	core_write(priv, CORE_PLL_GROUP6, RG_LCDDS_PCW_NCPO0(0));
 	core_write(priv, CORE_PLL_GROUP10, RG_LCDDS_SSC_DELTA(ssc_delta));
@@ -478,6 +473,8 @@ mt7530_pad_clk_setup(struct dsa_switch *ds, phy_interface_t interface)
 	core_write(priv, CORE_PLL_GROUP7,
 		   RG_LCDDS_PCW_NCPO_CHG | RG_LCCDS_C(3) |
 		   RG_LCDDS_PWDB | RG_LCDDS_ISO_EN);
+
+	/* Enable MT7530 core and TRGMII Tx clocks */
 	core_set(priv, CORE_TRGMII_GSW_CLK_CG,
 		 REG_GSWCK_EN | REG_TRGMIICK_EN);