linux-kernel - [PATCH v2 1/2] i2c: smbus: introduce Write Disable-aware SPD instantiating functions

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Message-Id: <20250430-for-upstream-i801-spd5118-no-instantiate-v2-1-2f54d91ae2c7@canonical.com>
Date: Wed, 30 Apr 2025 19:26:16 +0800
From: "Yo-Jung (Leo) Lin" <leo.lin@...onical.com>
To: Jean Delvare <jdelvare@...e.com>, Andi Shyti <andi.shyti@...nel.org>, 
 Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc: Guenter Roeck <linux@...ck-us.net>, 
 "Chia-Lin Kao (AceLan)" <acelan.kao@...onical.com>, 
 linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org, 
 "Yo-Jung Lin (Leo)" <leo.lin@...onical.com>
Subject: [PATCH v2 1/2] 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 (Leo) Lin <leo.lin@...onical.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 48e1af544b75..a7f89946dad4 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/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;
 }
diff --git a/drivers/i2c/busses/i2c-piix4.c b/drivers/i2c/busses/i2c-piix4.c
index dd75916157f0..56839557ec6c 100644
--- a/drivers/i2c/busses/i2c-piix4.c
+++ b/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;
diff --git a/drivers/i2c/i2c-smbus.c b/drivers/i2c/i2c-smbus.c
index 7d40e7aa3799..0316b347f9e7 100644
--- a/drivers/i2c/i2c-smbus.c
+++ b/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@...e.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 */

-- 
2.43.0