Date:   Tue, 21 Mar 2023 10:16:39 -0500
From:   Eddie James <eajames@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-aspeed@...ts.ozlabs.org, devicetree@...r.kernel.org,
        andrew@...id.au, joel@....id.au, krzysztof.kozlowski+dt@...aro.org,
        robh+dt@...nel.org, arnd@...db.de, gregkh@...uxfoundation.org,
        Eddie James <eajames@...ux.ibm.com>
Subject: [PATCH v2 1/4] eeprom: ee1004: Enable devices on multiple busses

The driver previously prevented probing devices on more than one
bus due to locking constraints with the special page addresses. This
constraint can be removed by allocating a reference-counted bus
structure containing the lock, rather than using global variables.

Signed-off-by: Eddie James <eajames@...ux.ibm.com>
---
 drivers/misc/eeprom/ee1004.c | 175 +++++++++++++++++++++--------------
 1 file changed, 106 insertions(+), 69 deletions(-)

diff --git a/drivers/misc/eeprom/ee1004.c b/drivers/misc/eeprom/ee1004.c
index c8c6deb7ed89..950813821087 100644
--- a/drivers/misc/eeprom/ee1004.c
+++ b/drivers/misc/eeprom/ee1004.c
@@ -9,12 +9,15 @@
  * Copyright (C) 2008 Wolfram Sang, Pengutronix
  */
 
+#include <linux/err.h>
 #include <linux/i2c.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
+#include <linux/list.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/of_device.h>
 
 /*
  * DDR4 memory modules use special EEPROMs following the Jedec EE1004
@@ -31,20 +34,24 @@
  * over performance.
  */
 
-#define EE1004_ADDR_SET_PAGE		0x36
+#define EE1004_ADDR_SET_PAGE0		0x36
+#define EE1004_ADDR_SET_PAGE1		0x37
 #define EE1004_NUM_PAGES		2
 #define EE1004_PAGE_SIZE		256
 #define EE1004_PAGE_SHIFT		8
 #define EE1004_EEPROM_SIZE		(EE1004_PAGE_SIZE * EE1004_NUM_PAGES)
 
-/*
- * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
- * from page selection to end of read.
- */
-static DEFINE_MUTEX(ee1004_bus_lock);
-static struct i2c_client *ee1004_set_page[EE1004_NUM_PAGES];
-static unsigned int ee1004_dev_count;
-static int ee1004_current_page;
+struct ee1004_bus {
+	struct kref kref;
+	struct list_head list;
+	struct mutex lock;
+	struct i2c_adapter *adapter;
+	struct i2c_client *set_page_clients[EE1004_NUM_PAGES];
+	int page;
+};
+
+static LIST_HEAD(ee1004_busses);
+static DEFINE_MUTEX(ee1004_busses_lock);
 
 static const struct i2c_device_id ee1004_ids[] = {
 	{ "ee1004", 0 },
@@ -54,11 +61,11 @@ MODULE_DEVICE_TABLE(i2c, ee1004_ids);
 
 /*-------------------------------------------------------------------------*/
 
-static int ee1004_get_current_page(void)
+static int ee1004_get_current_page(struct ee1004_bus *bus)
 {
 	int err;
 
-	err = i2c_smbus_read_byte(ee1004_set_page[0]);
+	err = i2c_smbus_read_byte(bus->set_page_clients[0]);
 	if (err == -ENXIO) {
 		/* Nack means page 1 is selected */
 		return 1;
@@ -72,33 +79,30 @@ static int ee1004_get_current_page(void)
 	return 0;
 }
 
-static int ee1004_set_current_page(struct device *dev, int page)
+static int ee1004_set_current_page(struct ee1004_bus *bus, int page)
 {
 	int ret;
 
-	if (page == ee1004_current_page)
+	if (page == bus->page)
 		return 0;
 
 	/* Data is ignored */
-	ret = i2c_smbus_write_byte(ee1004_set_page[page], 0x00);
+	ret = i2c_smbus_write_byte(bus->set_page_clients[page], 0x00);
+
 	/*
 	 * Don't give up just yet. Some memory modules will select the page
 	 * but not ack the command. Check which page is selected now.
 	 */
-	if (ret == -ENXIO && ee1004_get_current_page() == page)
+	if (ret == -ENXIO && ee1004_get_current_page(bus) == page)
 		ret = 0;
-	if (ret < 0) {
-		dev_err(dev, "Failed to select page %d (%d)\n", page, ret);
+	if (ret < 0)
 		return ret;
-	}
-
-	dev_dbg(dev, "Selected page %d\n", page);
-	ee1004_current_page = page;
 
+	bus->page = page;
 	return 0;
 }
 
-static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
+static ssize_t ee1004_eeprom_read(struct i2c_client *client, struct ee1004_bus *bus, char *buf,
 				  unsigned int offset, size_t count)
 {
 	int status, page;
@@ -106,9 +110,11 @@ static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
 	page = offset >> EE1004_PAGE_SHIFT;
 	offset &= (1 << EE1004_PAGE_SHIFT) - 1;
 
-	status = ee1004_set_current_page(&client->dev, page);
-	if (status)
+	status = ee1004_set_current_page(bus, page);
+	if (status) {
+		dev_err(&client->dev, "Failed to select page %d (%d)\n", page, status);
 		return status;
+	}
 
 	/* Can't cross page boundaries */
 	if (offset + count > EE1004_PAGE_SIZE)
@@ -125,6 +131,7 @@ static ssize_t eeprom_read(struct file *filp, struct kobject *kobj,
 			   char *buf, loff_t off, size_t count)
 {
 	struct i2c_client *client = kobj_to_i2c_client(kobj);
+	struct ee1004_bus *bus = i2c_get_clientdata(client);
 	size_t requested = count;
 	int ret = 0;
 
@@ -132,10 +139,10 @@ static ssize_t eeprom_read(struct file *filp, struct kobject *kobj,
 	 * Read data from chip, protecting against concurrent access to
 	 * other EE1004 SPD EEPROMs on the same adapter.
 	 */
-	mutex_lock(&ee1004_bus_lock);
+	mutex_lock(&bus->lock);
 
 	while (count) {
-		ret = ee1004_eeprom_read(client, buf, off, count);
+		ret = ee1004_eeprom_read(client, bus, buf, off, count);
 		if (ret < 0)
 			goto out;
 
@@ -144,7 +151,7 @@ static ssize_t eeprom_read(struct file *filp, struct kobject *kobj,
 		count -= ret;
 	}
 out:
-	mutex_unlock(&ee1004_bus_lock);
+	mutex_unlock(&bus->lock);
 
 	return ret < 0 ? ret : requested;
 }
@@ -158,18 +165,56 @@ static struct bin_attribute *ee1004_attrs[] = {
 
 BIN_ATTRIBUTE_GROUPS(ee1004);
 
-static void ee1004_cleanup(int idx)
+static void ee1004_bus_unregister(struct ee1004_bus *bus)
 {
-	if (--ee1004_dev_count == 0)
-		while (--idx >= 0) {
-			i2c_unregister_device(ee1004_set_page[idx]);
-			ee1004_set_page[idx] = NULL;
-		}
+	i2c_unregister_device(bus->set_page_clients[1]);
+	i2c_unregister_device(bus->set_page_clients[0]);
+}
+
+static void ee1004_bus_release(struct kref *kref)
+{
+	struct ee1004_bus *bus = container_of(kref, struct ee1004_bus, kref);
+
+	ee1004_bus_unregister(bus);
+
+	mutex_lock(&ee1004_busses_lock);
+	list_del(&bus->list);
+	mutex_unlock(&ee1004_busses_lock);
+
+	kfree(bus);
+}
+
+static int ee1004_bus_initialize(struct ee1004_bus *bus, struct i2c_adapter *adapter)
+{
+	bus->set_page_clients[0] = i2c_new_dummy_device(adapter, EE1004_ADDR_SET_PAGE0);
+	if (IS_ERR(bus->set_page_clients[0]))
+		return PTR_ERR(bus->set_page_clients[0]);
+
+	bus->set_page_clients[1] = i2c_new_dummy_device(adapter, EE1004_ADDR_SET_PAGE1);
+	if (IS_ERR(bus->set_page_clients[1])) {
+		i2c_unregister_device(bus->set_page_clients[0]);
+		return PTR_ERR(bus->set_page_clients[1]);
+	}
+
+	bus->page = ee1004_get_current_page(bus);
+	if (bus->page < 0) {
+		ee1004_bus_unregister(bus);
+		return bus->page;
+	}
+
+	kref_init(&bus->kref);
+	list_add(&bus->list, &ee1004_busses);
+	mutex_init(&bus->lock);
+	bus->adapter = adapter;
+
+	return 0;
 }
 
 static int ee1004_probe(struct i2c_client *client)
 {
-	int err, cnr = 0;
+	struct ee1004_bus *bus;
+	bool found = false;
+	int rc = 0;
 
 	/* Make sure we can operate on this adapter */
 	if (!i2c_check_functionality(client->adapter,
@@ -178,53 +223,45 @@ static int ee1004_probe(struct i2c_client *client)
 				     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
 		return -EPFNOSUPPORT;
 
-	/* Use 2 dummy devices for page select command */
-	mutex_lock(&ee1004_bus_lock);
-	if (++ee1004_dev_count == 1) {
-		for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
-			struct i2c_client *cl;
-
-			cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr);
-			if (IS_ERR(cl)) {
-				err = PTR_ERR(cl);
-				goto err_clients;
-			}
-			ee1004_set_page[cnr] = cl;
+	mutex_lock(&ee1004_busses_lock);
+	list_for_each_entry(bus, &ee1004_busses, list) {
+		if (bus->adapter == client->adapter) {
+			kref_get(&bus->kref);
+			found = true;
+			break;
+		}
+	}
+
+	if (!found) {
+		bus = kzalloc(sizeof(*bus), GFP_KERNEL);
+		if (!bus) {
+			rc = -ENOMEM;
+			goto unlock;
 		}
 
-		/* Remember current page to avoid unneeded page select */
-		err = ee1004_get_current_page();
-		if (err < 0)
-			goto err_clients;
-		dev_dbg(&client->dev, "Currently selected page: %d\n", err);
-		ee1004_current_page = err;
-	} else if (client->adapter != ee1004_set_page[0]->adapter) {
-		dev_err(&client->dev,
-			"Driver only supports devices on a single I2C bus\n");
-		err = -EOPNOTSUPP;
-		goto err_clients;
+		rc = ee1004_bus_initialize(bus, client->adapter);
+		if (rc) {
+			kfree(bus);
+			goto unlock;
+		}
 	}
-	mutex_unlock(&ee1004_bus_lock);
+
+	i2c_set_clientdata(client, bus);
 
 	dev_info(&client->dev,
 		 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
 		 EE1004_EEPROM_SIZE);
 
-	return 0;
-
- err_clients:
-	ee1004_cleanup(cnr);
-	mutex_unlock(&ee1004_bus_lock);
-
-	return err;
+unlock:
+	mutex_unlock(&ee1004_busses_lock);
+	return rc;
 }
 
 static void ee1004_remove(struct i2c_client *client)
 {
-	/* Remove page select clients if this is the last device */
-	mutex_lock(&ee1004_bus_lock);
-	ee1004_cleanup(EE1004_NUM_PAGES);
-	mutex_unlock(&ee1004_bus_lock);
+	struct ee1004_bus *bus = i2c_get_clientdata(client);
+
+	kref_put(&bus->kref, ee1004_bus_release);
 }
 
 /*-------------------------------------------------------------------------*/
-- 
2.31.1

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