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Date: Tue, 5 Mar 2024 21:28:08 +0100
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From: Heiner Kallweit <hkall@kernel.org>
Subject: [PATCH RFT] i2c: i801: Call i2c_register_spd for muxed child segments
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To: "linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Cc: Wolfram Sang <wsa@kernel.org>
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So far i2c_register_spd() is supported only on systems with up to
8 memory slots. Reason is that on a single SMBus only 8 SPD EEPROMS
can be addressed. The following patch adds support for calling
i2c_register_spd() on multiplexed SMBUS segments.

Out-of-the-box only certain ASUS Z8 systems are supported.
See mux_dmi_table[] in the i801 driver.
These systems seem to be quite rare nowadays, so I'd appreciate
if the owner of such a system could test the patch.

For each DIMM module a message like the following should appear in dmesg.
i2c i2c-11: Successfully instantiated SPD at 0x50
A response including the full dmesg log would be perfect.

For other systems with >8 memory slots, where the SMBUS is GPIO-muxed,
it should be possible to add an appropriate entry to mux_dmi_table[].
Then the patch should work as expected on such a system too.

Note: This patch is applicable only after 8821c8376993 ("i2c: smbus:
Prepare i2c_register_spd for usage on muxed segments").
This patch showed up in linux-next from March 5th 2024.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
 drivers/i2c/busses/i2c-i801.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index 8f225cd7b..4b9d04f20 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -105,6 +105,7 @@
 #include <linux/ioport.h>
 #include <linux/init.h>
 #include <linux/i2c.h>
+#include <linux/i2c-mux.h>
 #include <linux/i2c-smbus.h>
 #include <linux/acpi.h>
 #include <linux/io.h>
@@ -291,6 +292,7 @@ struct i801_priv {
 #if IS_ENABLED(CONFIG_I2C_MUX_GPIO) && defined CONFIG_DMI
 	struct platform_device *mux_pdev;
 	struct gpiod_lookup_table *lookup;
+	struct notifier_block mux_notifier_block;
 #endif
 	struct platform_device *tco_pdev;
 
@@ -1388,6 +1390,23 @@ static const struct dmi_system_id mux_dmi_table[] = {
 	{ }
 };
 
+static int i801_notifier_call(struct notifier_block *nb, unsigned long action,
+			      void *data)
+{
+	struct i801_priv *priv = container_of(nb, struct i801_priv, mux_notifier_block);
+	struct device *dev = data;
+
+	if (action != BUS_NOTIFY_ADD_DEVICE ||
+	    dev->type != &i2c_adapter_type ||
+	    i2c_root_adapter(dev) != &priv->adapter)
+		return NOTIFY_DONE;
+
+	/* Call i2c_register_spd for muxed child segments */
+	i2c_register_spd(to_i2c_adapter(dev));
+
+	return NOTIFY_OK;
+}
+
 /* Setup multiplexing if needed */
 static void i801_add_mux(struct i801_priv *priv)
 {
@@ -1425,6 +1444,9 @@ static void i801_add_mux(struct i801_priv *priv)
 	gpiod_add_lookup_table(lookup);
 	priv->lookup = lookup;
 
+	priv->mux_notifier_block.notifier_call = i801_notifier_call;
+	if (bus_register_notifier(&i2c_bus_type, &priv->mux_notifier_block))
+		return;
 	/*
 	 * Register the mux device, we use PLATFORM_DEVID_NONE here
 	 * because since we are referring to the GPIO chip by name we are
@@ -1443,6 +1465,7 @@ static void i801_add_mux(struct i801_priv *priv)
 
 static void i801_del_mux(struct i801_priv *priv)
 {
+	bus_unregister_notifier(&i2c_bus_type, &priv->mux_notifier_block);
 	platform_device_unregister(priv->mux_pdev);
 	gpiod_remove_lookup_table(priv->lookup);
 }
-- 
2.44.0