[PATCH 1/2] igc: Wait for MAC passthrough after reset

[Chia-Lin Kao (AceLan)]

Some systems support MAC passthrough for dock Ethernet controllers by
having firmware rewrite the receive address registers after the controller
reset completes.

igc resets the controller before reading RAL0/RAH0, so that reset can
restore the controller native MAC address temporarily. If the driver reads
the registers immediately, it can race the firmware rewrite and keep the
native dock MAC instead of the host passthrough MAC.

For LMVP devices, poll RAL0/RAH0 after reset and before reading the MAC
address. Stop once the address registers change to another valid Ethernet
address, allowing firmware a bounded window to complete the passthrough
update.

Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao@xxxxxxxxxxxxx>
---
 drivers/net/ethernet/intel/igc/igc_main.c | 48 +++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 2c9e2dfd8499..fa9752ed8bc5 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -11,6 +11,7 @@
 #include <net/pkt_sched.h>
 #include <linux/bpf_trace.h>
 #include <net/xdp_sock_drv.h>
+#include <linux/etherdevice.h>
 #include <linux/pci.h>
 #include <linux/mdio.h>
 
@@ -69,6 +70,52 @@ static const struct pci_device_id igc_pci_tbl[] = {
 
 MODULE_DEVICE_TABLE(pci, igc_pci_tbl);
 
+static void igc_read_rar0(struct igc_hw *hw, u8 *addr, u32 *ral, u32 *rah)
+{
+	*ral = rd32(IGC_RAL(0));
+	*rah = rd32(IGC_RAH(0));
+
+	addr[0] = *ral & 0xff;
+	addr[1] = (*ral >> 8) & 0xff;
+	addr[2] = (*ral >> 16) & 0xff;
+	addr[3] = (*ral >> 24) & 0xff;
+	addr[4] = *rah & 0xff;
+	addr[5] = (*rah >> 8) & 0xff;
+}
+
+static bool igc_is_lmvp_device(struct pci_dev *pdev)
+{
+	switch (pdev->device) {
+	case IGC_DEV_ID_I225_LMVP:
+	case IGC_DEV_ID_I226_LMVP:
+		return true;
+	default:
+		return false;
+	}
+}
+
+static void igc_wait_for_lmvp_mac_passthrough(struct pci_dev *pdev,
+					      struct igc_hw *hw)
+{
+	u8 addr[ETH_ALEN] __aligned(2);
+	u32 orig_ral, orig_rah;
+	u32 ral, rah;
+	int i;
+
+	if (!igc_is_lmvp_device(pdev))
+		return;
+
+	igc_read_rar0(hw, addr, &orig_ral, &orig_rah);
+
+	for (i = 0; i < 100; i++) {
+		msleep(100);
+		igc_read_rar0(hw, addr, &ral, &rah);
+		if ((ral != orig_ral || rah != orig_rah) &&
+		    is_valid_ether_addr(addr))
+			return;
+	}
+}
+
 enum latency_range {
 	lowest_latency = 0,
 	low_latency = 1,
@@ -7259,6 +7306,7 @@ static int igc_probe(struct pci_dev *pdev,
 	 * known good starting state
 	 */
 	hw->mac.ops.reset_hw(hw);
+	igc_wait_for_lmvp_mac_passthrough(pdev, hw);
 
 	if (igc_get_flash_presence_i225(hw)) {
 		if (hw->nvm.ops.validate(hw) < 0) {
-- 
2.53.0