[SRU][N][PATCH 7/11] i2c: smbus: introduce Write Disable-aware SPD instantiating functions

[Alice C. Munduruca]

From: "Yo-Jung (Leo) Lin" <leo.lin at canonical.com>

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 at canonical.com>
Reviewed-by: Guenter Roeck <linux at 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 at kernel.org>
(cherry picked from commit 4d6d35d3417dcab14a9b1b9771c3cd62e8ed442b)
BugLink: https://bugs.launchpad.net/bugs/2114963
Signed-off-by: Alice C. Munduruca <alice.munduruca at canonical.com>
---
 drivers/i2c/busses/i2c-i801.c  |  4 ++--
 drivers/i2c/busses/i2c-piix4.c |  2 +-
 drivers/i2c/i2c-smbus.c        | 21 +++++++++++++++++++--
 include/linux/i2c-smbus.h      |  6 ++++--
 4 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index 61b136cd571e..1d6963852981 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -1299,7 +1299,7 @@ static void i801_probe_optional_slaves(struct i801_priv *priv)
 #if IS_ENABLED(CONFIG_I2C_MUX_GPIO)
 	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) {}
@@ -1404,7 +1404,7 @@ 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;
 }
diff --git a/drivers/i2c/busses/i2c-piix4.c b/drivers/i2c/busses/i2c-piix4.c
index 5af934617810..551739079b1d 100644
--- a/drivers/i2c/busses/i2c-piix4.c
+++ b/drivers/i2c/busses/i2c-piix4.c
@@ -989,7 +989,7 @@ 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;
diff --git a/drivers/i2c/i2c-smbus.c b/drivers/i2c/i2c-smbus.c
index c11486bf56f1..e2752127585b 100644
--- a/drivers/i2c/i2c-smbus.c
+++ b/drivers/i2c/i2c-smbus.c
@@ -362,12 +362,13 @@ 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) {
@@ -430,6 +431,7 @@ 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,
@@ -453,6 +455,9 @@ 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",
@@ -461,7 +466,19 @@ 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 at suse.de>");
diff --git a/include/linux/i2c-smbus.h b/include/linux/i2c-smbus.h
index ced1c6ead52a..dc1bd2ab4c13 100644
--- a/include/linux/i2c-smbus.h
+++ b/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 */
-- 
2.48.1