net: fec: fix MDIO probing for some FEC hardware blocks

Some (apparently older) versions of the FEC hardware block do not like
the MMFR register being cleared to avoid generation of MII events at
initialization time. The action of clearing this register results in no
future MII events being generated at all on the problem block. This means
the probing of the MDIO bus will find no PHYs.

Create a quirk that can be checked at the FECs MII init time so that
the right thing is done. The quirk is set as appropriate for the FEC
hardware blocks that are known to need this.

Fixes: f166f890 ("net: ethernet: fec: Replace interrupt driven MDIO with polled IO")
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>
Acked-by: Fugang Duan <fugand.duan@nxp.com>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Clemens Gruber <clemens.gruber@pqgruber.com>
Link: https://lore.kernel.org/r/20201028052232.1315167-1-gerg@linux-m68k.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/freescale/fec.h

@@ -456,6 +456,12 @@ struct bufdesc_ex {
  */
 #define FEC_QUIRK_HAS_FRREG		(1 << 16)
 
+/* Some FEC hardware blocks need the MMFR cleared at setup time to avoid
+ * the generation of an MII event. This must be avoided in the older
+ * FEC blocks where it will stop MII events being generated.
+ */
+#define FEC_QUIRK_CLEAR_SETUP_MII	(1 << 17)
+
 struct bufdesc_prop {
 	int qid;
 	/* Address of Rx and Tx buffers */

drivers/net/ethernet/freescale/fec_main.c

@@ -100,14 +100,14 @@ static const struct fec_devinfo fec_imx27_info = {
 static const struct fec_devinfo fec_imx28_info = {
 	.quirks = FEC_QUIRK_ENET_MAC | FEC_QUIRK_SWAP_FRAME |
 		  FEC_QUIRK_SINGLE_MDIO | FEC_QUIRK_HAS_RACC |
-		  FEC_QUIRK_HAS_FRREG,
+		  FEC_QUIRK_HAS_FRREG | FEC_QUIRK_CLEAR_SETUP_MII,
 };
 
 static const struct fec_devinfo fec_imx6q_info = {
 	.quirks = FEC_QUIRK_ENET_MAC | FEC_QUIRK_HAS_GBIT |
 		  FEC_QUIRK_HAS_BUFDESC_EX | FEC_QUIRK_HAS_CSUM |
 		  FEC_QUIRK_HAS_VLAN | FEC_QUIRK_ERR006358 |
-		  FEC_QUIRK_HAS_RACC,
+		  FEC_QUIRK_HAS_RACC | FEC_QUIRK_CLEAR_SETUP_MII,
 };
 
 static const struct fec_devinfo fec_mvf600_info = {
@@ -119,7 +119,8 @@ static const struct fec_devinfo fec_imx6x_info = {
 		  FEC_QUIRK_HAS_BUFDESC_EX | FEC_QUIRK_HAS_CSUM |
 		  FEC_QUIRK_HAS_VLAN | FEC_QUIRK_HAS_AVB |
 		  FEC_QUIRK_ERR007885 | FEC_QUIRK_BUG_CAPTURE |
-		  FEC_QUIRK_HAS_RACC | FEC_QUIRK_HAS_COALESCE,
+		  FEC_QUIRK_HAS_RACC | FEC_QUIRK_HAS_COALESCE |
+		  FEC_QUIRK_CLEAR_SETUP_MII,
 };
 
 static const struct fec_devinfo fec_imx6ul_info = {
@@ -127,7 +128,7 @@ static const struct fec_devinfo fec_imx6ul_info = {
 		  FEC_QUIRK_HAS_BUFDESC_EX | FEC_QUIRK_HAS_CSUM |
 		  FEC_QUIRK_HAS_VLAN | FEC_QUIRK_ERR007885 |
 		  FEC_QUIRK_BUG_CAPTURE | FEC_QUIRK_HAS_RACC |
-		  FEC_QUIRK_HAS_COALESCE,
+		  FEC_QUIRK_HAS_COALESCE | FEC_QUIRK_CLEAR_SETUP_MII,
 };
 
 static struct platform_device_id fec_devtype[] = {
@@ -2134,15 +2135,17 @@ static int fec_enet_mii_init(struct platform_device *pdev)
 	if (suppress_preamble)
 		fep->phy_speed |= BIT(7);
 
-	/* Clear MMFR to avoid to generate MII event by writing MSCR.
-	 * MII event generation condition:
-	 * - writing MSCR:
-	 *	- mmfr[31:0]_not_zero & mscr[7:0]_is_zero &
-	 *	  mscr_reg_data_in[7:0] != 0
-	 * - writing MMFR:
-	 *	- mscr[7:0]_not_zero
-	 */
-	writel(0, fep->hwp + FEC_MII_DATA);
+	if (fep->quirks & FEC_QUIRK_CLEAR_SETUP_MII) {
+		/* Clear MMFR to avoid to generate MII event by writing MSCR.
+		 * MII event generation condition:
+		 * - writing MSCR:
+		 *	- mmfr[31:0]_not_zero & mscr[7:0]_is_zero &
+		 *	  mscr_reg_data_in[7:0] != 0
+		 * - writing MMFR:
+		 *	- mscr[7:0]_not_zero
+		 */
+		writel(0, fep->hwp + FEC_MII_DATA);
+	}
 
 	writel(fep->phy_speed, fep->hwp + FEC_MII_SPEED);