memory_accessor: implement the new memory_accessor interface for I2C EEPROM

In the case of at24, the platform code registers a 'setup' callback with
the at24_platform_data. When the at24 driver detects an EEPROM, it fills
out the read and write functions of the memory_accessor and calls the
setup callback passing the memory_accessor struct. The platform code can
then use the read/write functions in the memory_accessor struct for
reading and writing the EEPROM.

Signed-off-by: Kevin Hilman <[e-mail]>
Cc: David Brownell <[e-mail]>
Cc: Jean Delvare <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/misc/eeprom/at24.c

···
 
 struct at24_data {
 	struct at24_platform_data chip;
+	struct memory_accessor macc;
 	bool use_smbus;
 
 	/*
···
 		return status;
 }
 
-static ssize_t at24_bin_read(struct kobject *kobj, struct bin_attribute *attr,
+static ssize_t at24_read(struct at24_data *at24,
 		char *buf, loff_t off, size_t count)
 {
-	struct at24_data *at24;
 	ssize_t retval = 0;
-
-	at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));
 
 	if (unlikely(!count))
 		return count;
···
 	return retval;
 }
 
+static ssize_t at24_bin_read(struct kobject *kobj, struct bin_attribute *attr,
+		char *buf, loff_t off, size_t count)
+{
+	struct at24_data *at24;
 
-/*
- * REVISIT: export at24_bin{read,write}() to let other kernel code use
- * eeprom data. For example, it might hold a board's Ethernet address, or
- * board-specific calibration data generated on the manufacturing floor.
- */
+	at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));
+	return at24_read(at24, buf, off, count);
+}
 
 
 /*
···
 	return -ETIMEDOUT;
 }
 
-static ssize_t at24_bin_write(struct kobject *kobj, struct bin_attribute *attr,
+static ssize_t at24_write(struct at24_data *at24,
 		char *buf, loff_t off, size_t count)
 {
-	struct at24_data *at24;
 	ssize_t retval = 0;
-
-	at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));
 
 	if (unlikely(!count))
 		return count;
···
 	mutex_unlock(&at24->lock);
 
 	return retval;
+}
+
+static ssize_t at24_bin_write(struct kobject *kobj, struct bin_attribute *attr,
+		char *buf, loff_t off, size_t count)
+{
+	struct at24_data *at24;
+
+	at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));
+	return at24_write(at24, buf, off, count);
+}
+
+/*-------------------------------------------------------------------------*/
+
+/*
+ * This lets other kernel code access the eeprom data. For example, it
+ * might hold a board's Ethernet address, or board-specific calibration
+ * data generated on the manufacturing floor.
+ */
+
+static ssize_t at24_macc_read(struct memory_accessor *macc, char *buf,
+			 off_t offset, size_t count)
+{
+	struct at24_data *at24 = container_of(macc, struct at24_data, macc);
+
+	return at24_read(at24, buf, offset, count);
+}
+
+static ssize_t at24_macc_write(struct memory_accessor *macc, char *buf,
+			  off_t offset, size_t count)
+{
+	struct at24_data *at24 = container_of(macc, struct at24_data, macc);
+
+	return at24_write(at24, buf, offset, count);
 }
 
 /*-------------------------------------------------------------------------*/
···
 		 * is recommended anyhow.
 		 */
 		chip.page_size = 1;
+
+		chip.setup = NULL;
+		chip.context = NULL;
 	}
 
 	if (!is_power_of_2(chip.byte_len))
···
 	at24->bin.read = at24_bin_read;
 	at24->bin.size = chip.byte_len;
 
+	at24->macc.read = at24_macc_read;
+
 	writable = !(chip.flags & AT24_FLAG_READONLY);
 	if (writable) {
 		if (!use_smbus || i2c_check_functionality(client->adapter,
 				I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {
 
 			unsigned write_max = chip.page_size;
+
+			at24->macc.write = at24_macc_write;
 
 			at24->bin.write = at24_bin_write;
 			at24->bin.attr.mode |= S_IWUSR;
···
 		chip.page_size, num_addresses,
 		at24->write_max,
 		use_smbus ? ", use_smbus" : "");
+
+	/* export data to kernel code */
+	if (chip.setup)
+		chip.setup(&at24->macc, chip.context);
 
 	return 0;
 

include/linux/i2c/at24.h

···
 #define _LINUX_AT24_H
 
 #include <linux/types.h>
+#include <linux/memory.h>
 
 /*
  * As seen through Linux I2C, differences between the most common types of I2C
···
 #define AT24_FLAG_READONLY	0x40	/* sysfs-entry will be read-only */
 #define AT24_FLAG_IRUGO		0x20	/* sysfs-entry will be world-readable */
 #define AT24_FLAG_TAKE8ADDR	0x10	/* take always 8 addresses (24c00) */
+
+	void		(*setup)(struct memory_accessor *, void *context);
+	void		*context;
 };
 
 #endif /* _LINUX_AT24_H */