[PATCH 3/4 v2] i2c: smbus: Add a way to instantiate SPD EEPROMs automatically

[Jean Delvare <jdelvare@suse.de>]

In simple cases we can instantiate SPD EEPROMs on the SMBus
automatically. Start with just DDR2, DDR3 and DDR4 on x86 for now,
and only for systems with no more than 4 memory slots. These
limitations may be lifted later.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
---
Changes since v1:
 * Fixed build warning reported by kbuild test bot

 drivers/i2c/i2c-smbus.c   |  104 +++++++++++++++++++++++++++++++++++++++++++++-
 include/linux/i2c-smbus.h |    8 +++
 2 files changed, 110 insertions(+), 2 deletions(-)

--- linux-5.3.orig/drivers/i2c/i2c-smbus.c	2019-10-14 11:33:20.372781769 +0200
+++ linux-5.3/drivers/i2c/i2c-smbus.c	2019-10-14 16:42:12.815302881 +0200
@@ -3,10 +3,11 @@
  * i2c-smbus.c - SMBus extensions to the I2C protocol
  *
  * Copyright (C) 2008 David Brownell
- * Copyright (C) 2010 Jean Delvare <jdelvare@suse.de>
+ * Copyright (C) 2010-2019 Jean Delvare <jdelvare@suse.de>
  */
 
 #include <linux/device.h>
+#include <linux/dmi.h>
 #include <linux/i2c.h>
 #include <linux/i2c-smbus.h>
 #include <linux/interrupt.h>
@@ -203,6 +204,107 @@ EXPORT_SYMBOL_GPL(i2c_handle_smbus_alert
 
 module_i2c_driver(smbalert_driver);
 
+/*
+ * SPD is not part of SMBus but we include it here for convenience as the
+ * target systems are the same.
+ * Restrictions to automatic SPD instantiation:
+ *  - Only works if all filled slots have the same memory type
+ *  - Only works for DDR2, DDR3 and DDR4 for now
+ *  - Only works on systems with 1 to 4 memory slots
+ */
+#if IS_ENABLED(CONFIG_DMI)
+void i2c_register_spd(struct i2c_adapter *adap)
+{
+	int n, slot_count = 0, dimm_count = 0;
+	u16 handle;
+	u8 common_mem_type = 0x0, mem_type;
+	u64 mem_size;
+	const char *name;
+
+	while ((handle = dmi_memdev_handle(slot_count)) != 0xffff) {
+		slot_count++;
+
+		/* Skip empty slots */
+		mem_size = dmi_memdev_size(handle);
+		if (!mem_size)
+			continue;
+
+		/* Skip undefined memory type */
+		mem_type = dmi_memdev_type(handle);
+		if (mem_type <= 0x02)		/* Invalid, Other, Unknown */
+			continue;
+
+		if (!common_mem_type) {
+			/* First filled slot */
+			common_mem_type = mem_type;
+		} else {
+			/* Check that all filled slots have the same type */
+			if (mem_type != common_mem_type) {
+				dev_warn(&adap->dev,
+					 "Different memory types mixed, not instantiating SPD\n");
+				return;
+			}
+		}
+		dimm_count++;
+	}
+
+	/* No useful DMI data, bail out */
+	if (!dimm_count)
+		return;
+
+	dev_info(&adap->dev, "%d/%d memory slots populated (from DMI)\n",
+		 dimm_count, slot_count);
+
+	if (slot_count > 4) {
+		dev_warn(&adap->dev,
+			 "Systems with more than 4 memory slots not supported yet, not instantiating SPD\n");
+		return;
+	}
+
+	switch (common_mem_type) {
+	case 0x13:	/* DDR2 */
+	case 0x18:	/* DDR3 */
+	case 0x1C:	/* LPDDR2 */
+	case 0x1D:	/* LPDDR3 */
+		name = "spd";
+		break;
+	case 0x1A:	/* DDR4 */
+	case 0x1E:	/* LPDDR4 */
+		name = "ee1004";
+		break;
+	default:
+		dev_info(&adap->dev,
+			 "Memory type 0x%02x not supported yet, not instantiating SPD\n",
+			 common_mem_type);
+		return;
+	}
+
+	/*
+	 * We don't know in which slots the memory modules are. We could
+	 * try to guess from the slot names, but that would be rather complex
+	 * and unreliable, so better probe all possible addresses until we
+	 * have found all memory modules.
+	 */
+	for (n = 0; n < slot_count && dimm_count; n++) {
+		struct i2c_board_info info;
+		unsigned short addr_list[2];
+
+		memset(&info, 0, sizeof(struct i2c_board_info));
+		strlcpy(info.type, name, I2C_NAME_SIZE);
+		addr_list[0] = 0x50 + n;
+		addr_list[1] = I2C_CLIENT_END;
+
+		if (i2c_new_probed_device(adap, &info, addr_list, NULL)) {
+			dev_info(&adap->dev,
+				 "Successfully instantiated SPD at 0x%hx\n",
+				 addr_list[0]);
+			dimm_count--;
+		}
+	}
+}
+EXPORT_SYMBOL_GPL(i2c_register_spd);
+#endif
+
 MODULE_AUTHOR("Jean Delvare <jdelvare@suse.de>");
 MODULE_DESCRIPTION("SMBus protocol extensions support");
 MODULE_LICENSE("GPL");
--- linux-5.3.orig/include/linux/i2c-smbus.h	2019-10-14 11:33:20.372781769 +0200
+++ linux-5.3/include/linux/i2c-smbus.h	2019-10-14 16:44:22.636959738 +0200
@@ -2,7 +2,7 @@
 /*
  * i2c-smbus.h - SMBus extensions to the I2C protocol
  *
- * Copyright (C) 2010 Jean Delvare <jdelvare@suse.de>
+ * Copyright (C) 2010-2019 Jean Delvare <jdelvare@suse.de>
  */
 
 #ifndef _LINUX_I2C_SMBUS_H
@@ -44,4 +44,10 @@ static inline int of_i2c_setup_smbus_ale
 }
 #endif
 
+#if IS_ENABLED(CONFIG_I2C_SMBUS) && IS_ENABLED(CONFIG_DMI)
+void i2c_register_spd(struct i2c_adapter *adap);
+#else
+static inline void i2c_register_spd(struct i2c_adapter *adap) { }
+#endif
+
 #endif /* _LINUX_I2C_SMBUS_H */

-- 
Jean Delvare
SUSE L3 Support