i2c: smbus: introduce Write Disable-aware SPD instantiating functions

Some SMBus controllers may restrict writes to addresses where SPD sensors
may reside. This may lead to some SPD sensors not functioning correctly,
and might need extra handling. Introduce new SPD-instantiating functions
that are aware of this, and use them instead.

Signed-off-by: Yo-Jung Lin (Leo) <leo.lin@canonical.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20250430-for-upstream-i801-spd5118-no-instantiate-v2-1-2f54d91ae2c7@canonical.com
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>

Author: 0xff07

drivers/i2c/busses/i2c-i801.c

@@ -1180,7 +1180,7 @@ static void i801_probe_optional_targets(struct i801_priv *priv)
 #ifdef CONFIG_I2C_I801_MUX
 	if (!priv->mux_pdev)
 #endif
-		i2c_register_spd(&priv->adapter);
+		i2c_register_spd_write_enable(&priv->adapter);
 }
 #else
 static void __init input_apanel_init(void) {}
@@ -1283,7 +1283,7 @@ static int i801_notifier_call(struct notifier_block *nb, unsigned long action,
 		return NOTIFY_DONE;
 
 	/* Call i2c_register_spd for muxed child segments */
-	i2c_register_spd(to_i2c_adapter(dev));
+	i2c_register_spd_write_enable(to_i2c_adapter(dev));
 
 	return NOTIFY_OK;
 }

drivers/i2c/busses/i2c-piix4.c

@@ -971,7 +971,7 @@ static int piix4_add_adapter(struct pci_dev *dev, unsigned short smba,
 	 * This would allow the ee1004 to be probed incorrectly.
 	 */
 	if (port == 0)
-		i2c_register_spd(adap);
+		i2c_register_spd_write_enable(adap);
 
 	*padap = adap;
 	return 0;

drivers/i2c/i2c-smbus.c

@@ -372,12 +372,13 @@ EXPORT_SYMBOL_GPL(i2c_free_slave_host_notify_device);
  *  - Only works on systems with 1 to 8 memory slots
  */
 #if IS_ENABLED(CONFIG_DMI)
-void i2c_register_spd(struct i2c_adapter *adap)
+static void i2c_register_spd(struct i2c_adapter *adap, bool write_disabled)
 {
 	int n, slot_count = 0, dimm_count = 0;
 	u16 handle;
 	u8 common_mem_type = 0x0, mem_type;
 	u64 mem_size;
+	bool instantiate = true;
 	const char *name;
 
 	while ((handle = dmi_memdev_handle(slot_count)) != 0xffff) {
@@ -438,6 +439,7 @@ void i2c_register_spd(struct i2c_adapter *adap)
 	case 0x22:	/* DDR5 */
 	case 0x23:	/* LPDDR5 */
 		name = "spd5118";
+		instantiate = !write_disabled;
 		break;
 	default:
 		dev_info(&adap->dev,
@@ -461,6 +463,9 @@ void i2c_register_spd(struct i2c_adapter *adap)
 		addr_list[0] = 0x50 + n;
 		addr_list[1] = I2C_CLIENT_END;
 
+		if (!instantiate)
+			continue;
+
 		if (!IS_ERR(i2c_new_scanned_device(adap, &info, addr_list, NULL))) {
 			dev_info(&adap->dev,
 				 "Successfully instantiated SPD at 0x%hx\n",
@@ -469,7 +474,19 @@ void i2c_register_spd(struct i2c_adapter *adap)
 		}
 	}
 }
-EXPORT_SYMBOL_GPL(i2c_register_spd);
+
+void i2c_register_spd_write_disable(struct i2c_adapter *adap)
+{
+	i2c_register_spd(adap, true);
+}
+EXPORT_SYMBOL_GPL(i2c_register_spd_write_disable);
+
+void i2c_register_spd_write_enable(struct i2c_adapter *adap)
+{
+	i2c_register_spd(adap, false);
+}
+EXPORT_SYMBOL_GPL(i2c_register_spd_write_enable);
+
 #endif
 
 MODULE_AUTHOR("Jean Delvare <jdelvare@suse.de>");

include/linux/i2c-smbus.h

@@ -44,9 +44,11 @@ static inline void i2c_free_slave_host_notify_device(struct i2c_client *client)
 #endif
 
 #if IS_ENABLED(CONFIG_I2C_SMBUS) && IS_ENABLED(CONFIG_DMI)
-void i2c_register_spd(struct i2c_adapter *adap);
+void i2c_register_spd_write_disable(struct i2c_adapter *adap);
+void i2c_register_spd_write_enable(struct i2c_adapter *adap);
 #else
-static inline void i2c_register_spd(struct i2c_adapter *adap) { }
+static inline void i2c_register_spd_write_disable(struct i2c_adapter *adap) { }
+static inline void i2c_register_spd_write_enable(struct i2c_adapter *adap) { }
 #endif
 
 #endif /* _LINUX_I2C_SMBUS_H */