net: pcs: xpcs: add support for NXP SJA1105

The NXP SJA1105 DSA switch integrates a Synopsys SGMII XPCS on port 4.
The generic code works fine, except there is an integration issue which
needs to be dealt with: in this switch, the XPCS is integrated with a
PMA that has the TX lane polarity inverted by default (PLUS is MINUS,
MINUS is PLUS).

To obtain normal non-inverted behavior, the TX lane polarity must be
inverted in the PCS, via the DIGITAL_CONTROL_2 register.

We introduce a pma_config() method in xpcs_compat which is called by the
phylink_pcs_config() implementation.

Also, the NXP SJA1105 returns all zeroes in the PHY ID registers 2 and 3.
We need to hack up an ad-hoc PHY ID (OUI is zero, device ID is 1) in
order for the XPCS driver to recognize it. This PHY ID is added to the
public include/linux/pcs/pcs-xpcs.h for that reason (for the sja1105
driver to be able to use it in a later patch).

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/net/pcs/pcs-xpcs-nxp.c b/drivers/net/pcs/pcs-xpcs-nxp.c
new file mode 100644
index 000000000000..51b2fc7d36a9
--- /dev/null
+++ b/drivers/net/pcs/pcs-xpcs-nxp.c
@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright 2021 NXP Semiconductors
+ */
+#include <linux/pcs/pcs-xpcs.h>
+#include "pcs-xpcs.h"
+
+/* In NXP SJA1105, the PCS is integrated with a PMA that has the TX lane
+ * polarity inverted by default (PLUS is MINUS, MINUS is PLUS). To obtain
+ * normal non-inverted behavior, the TX lane polarity must be inverted in the
+ * PCS, via the DIGITAL_CONTROL_2 register.
+ */
+int nxp_sja1105_sgmii_pma_config(struct dw_xpcs *xpcs)
+{
+	return xpcs_write(xpcs, MDIO_MMD_VEND2, DW_VR_MII_DIG_CTRL2,
+			  DW_VR_MII_DIG_CTRL2_TX_POL_INV);
+}