net: pse-pd: pd692x0: Preserve PSE configuration across reboots

Detect when PSE hardware is already configured (user byte == 42) and
skip hardware initialization to prevent power interruption to connected
devices during system reboots.

Previously, the driver would always reconfigure the PSE hardware on
probe, causing a port matrix reflash that resulted in temporary power
loss to all connected devices. This change maintains power continuity
by preserving existing configuration when the PSE has been previously
initialized.

Signed-off-by: Kory Maincent <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/pse-pd/pd692x0.c

···
 #define PD692X0_FW_MIN_VER	5
 #define PD692X0_FW_PATCH_VER	5
 
+#define PD692X0_USER_BYTE	42
+
 enum pd692x0_fw_state {
 	PD692X0_FW_UNKNOWN,
 	PD692X0_FW_OK,
···
 	PD692X0_MSG_GET_PORT_PARAM,
 	PD692X0_MSG_GET_POWER_BANK,
 	PD692X0_MSG_SET_POWER_BANK,
+	PD692X0_MSG_SET_USER_BYTE,
 
 	/* add new message above here */
 	PD692X0_MSG_CNT
···
 	bool last_cmd_key;
 	unsigned long last_cmd_key_time;
 
+	bool cfg_saved;
 	enum ethtool_c33_pse_admin_state admin_state[PD692X0_MAX_PIS];
 	struct regulator_dev *manager_reg[PD692X0_MAX_MANAGERS];
 	int manager_pw_budget[PD692X0_MAX_MANAGERS];
···
 	[PD692X0_MSG_SET_POWER_BANK] = {
 		.key = PD692X0_KEY_CMD,
 		.sub = {0x07, 0x0b, 0x57},
+	},
+	[PD692X0_MSG_SET_USER_BYTE] = {
+		.key = PD692X0_KEY_PRG,
+		.sub = {0x41, PD692X0_USER_BYTE},
+		.data = {0x4e, 0x4e, 0x4e, 0x4e,
+			 0x4e, 0x4e, 0x4e, 0x4e},
 	},
 };
 
···
 	}
 }
 
+static int
+pd692x0_save_user_byte(struct pd692x0_priv *priv)
+{
+	struct pd692x0_msg msg, buf;
+
+	msg = pd692x0_msg_template_list[PD692X0_MSG_SET_USER_BYTE];
+	return pd692x0_sendrecv_msg(priv, &msg, &buf);
+}
+
 static int pd692x0_setup_pi_matrix(struct pse_controller_dev *pcdev)
 {
 	struct pd692x0_priv *priv = to_pd692x0_priv(pcdev);
···
 	if (ret)
 		goto err_managers_req_pw;
 
-	ret = pd692x0_hw_conf_init(priv);
-	if (ret)
-		goto err_managers_req_pw;
+	/* Do not init the conf if it is already saved */
+	if (!priv->cfg_saved) {
+		ret = pd692x0_hw_conf_init(priv);
+		if (ret)
+			goto err_managers_req_pw;
+
+		ret = pd692x0_save_user_byte(priv);
+		if (ret)
+			goto err_managers_req_pw;
+	}
 
 	pd692x0_of_put_managers(priv, manager);
 	kfree(manager);
···
 			priv->fw_state = PD692X0_FW_OK;
 		}
 	}
+
+	if (buf.data[2] == PD692X0_USER_BYTE)
+		priv->cfg_saved = true;
 
 	priv->np = dev->of_node;
 	priv->pcdev.nr_lines = PD692X0_MAX_PIS;