[PATCH v1 net-next] net: lan743x: fix SGMII detection on PCI1xxxx B0+ during warm reset

[Thangaraj Samynathan <thangaraj.s@microchip.com>]

A warm reset on boards using an EEPROM-only strap configuration (where
no MAC address is set in the image) can cause the driver to incorrectly
revert to RGMII mode. This occurs because the ENET_CONFIG_LOAD_STARTED
bit may not persist or behave as expected.

Update pci11x1x_strap_get_status() to use revision-specific validation:

- For PCI11x1x A0: Continue using the legacy check (config load started
  or reset protection) to validate the SGMII strap.
- For PCI11x1x B0 and later: Use the newly available
  STRAP_READ_USE_SGMII_EN_ bit in the upper strap register to validate
  the lower SGMII_EN bit.

This ensures the SGMII interface is correctly identified even after a
warm reboot.

Signed-off-by: Thangaraj Samynathan <thangaraj.s@microchip.com>
---
v0 -> v1
	* Added helpers to check if the device revision is a0
---
 drivers/net/ethernet/microchip/lan743x_main.c | 15 +++++++++++----
 drivers/net/ethernet/microchip/lan743x_main.h |  1 +
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/microchip/lan743x_main.c b/drivers/net/ethernet/microchip/lan743x_main.c
index a3845edf0e48..83b640ab9d62 100644
--- a/drivers/net/ethernet/microchip/lan743x_main.c
+++ b/drivers/net/ethernet/microchip/lan743x_main.c
@@ -28,6 +28,12 @@
 
 #define RFE_RD_FIFO_TH_3_DWORDS	0x3
 
+static bool pci11x1x_is_a0(struct lan743x_adapter *adapter)
+{
+	u32 dev_rev = adapter->csr.id_rev & ID_REV_CHIP_REV_MASK_;
+	return dev_rev == ID_REV_CHIP_REV_PCI11X1X_A0_;
+}
+
 static void pci11x1x_strap_get_status(struct lan743x_adapter *adapter)
 {
 	u32 chip_rev;
@@ -47,10 +53,11 @@ static void pci11x1x_strap_get_status(struct lan743x_adapter *adapter)
 	cfg_load = lan743x_csr_read(adapter, ETH_SYS_CONFIG_LOAD_STARTED_REG);
 	lan743x_hs_syslock_release(adapter);
 	hw_cfg = lan743x_csr_read(adapter, HW_CFG);
-
-	if (cfg_load & GEN_SYS_LOAD_STARTED_REG_ETH_ ||
-	    hw_cfg & HW_CFG_RST_PROTECT_) {
-		strap = lan743x_csr_read(adapter, STRAP_READ);
+	strap = lan743x_csr_read(adapter, STRAP_READ);
+	if ((pci11x1x_is_a0(adapter) &&
+	     (cfg_load & GEN_SYS_LOAD_STARTED_REG_ETH_ ||
+	     hw_cfg & HW_CFG_RST_PROTECT_)) ||
+	     (strap & STRAP_READ_USE_SGMII_EN_)) {
 		if (strap & STRAP_READ_SGMII_EN_)
 			adapter->is_sgmii_en = true;
 		else
diff --git a/drivers/net/ethernet/microchip/lan743x_main.h b/drivers/net/ethernet/microchip/lan743x_main.h
index 02a28b709163..160d94a7cee6 100644
--- a/drivers/net/ethernet/microchip/lan743x_main.h
+++ b/drivers/net/ethernet/microchip/lan743x_main.h
@@ -27,6 +27,7 @@
 #define ID_REV_CHIP_REV_MASK_		(0x0000FFFF)
 #define ID_REV_CHIP_REV_A0_		(0x00000000)
 #define ID_REV_CHIP_REV_B0_		(0x00000010)
+#define ID_REV_CHIP_REV_PCI11X1X_A0_	(0x000000A0)
 #define ID_REV_CHIP_REV_PCI11X1X_B0_	(0x000000B0)
 
 #define FPGA_REV			(0x04)
-- 
2.34.1