hwmon: (pmbus/acbel-fsg032) Add firmware version debugfs attribute

Like the IBM CFFPS driver, export the PSU's firmware version to a
debugfs attribute as reported in the manufacturer register.
Signed-off-by: Eddie James <eajames@linux.ibm.com>
Link: https://lore.kernel.org/r/20230628153453.122213-1-eajames@linux.ibm.com
[groeck: Dropped unused variable; changed buffer from char to u8]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/acbel-fsg032.c

@@ -3,14 +3,51 @@
  * Copyright 2023 IBM Corp.
  */
 
+#include <linux/debugfs.h>
 #include <linux/device.h>
 #include <linux/fs.h>
 #include <linux/i2c.h>
+#include <linux/minmax.h>
 #include <linux/module.h>
 #include <linux/pmbus.h>
 #include <linux/hwmon-sysfs.h>
 #include "pmbus.h"
 
+#define ACBEL_MFR_FW_REVISION	0xd9
+
+static ssize_t acbel_fsg032_debugfs_read(struct file *file, char __user *buf, size_t count,
+					 loff_t *ppos)
+{
+	struct i2c_client *client = file->private_data;
+	u8 data[I2C_SMBUS_BLOCK_MAX + 2] = { 0 };
+	char out[8];
+	int rc;
+
+	rc = i2c_smbus_read_block_data(client, ACBEL_MFR_FW_REVISION, data);
+	if (rc < 0)
+		return rc;
+
+	rc = snprintf(out, sizeof(out), "%*phN\n", min(rc, 3), data);
+	return simple_read_from_buffer(buf, count, ppos, out, rc);
+}
+
+static const struct file_operations acbel_debugfs_ops = {
+	.llseek = noop_llseek,
+	.read = acbel_fsg032_debugfs_read,
+	.write = NULL,
+	.open = simple_open,
+};
+
+static void acbel_fsg032_init_debugfs(struct i2c_client *client)
+{
+	struct dentry *debugfs = pmbus_get_debugfs_dir(client);
+
+	if (!debugfs)
+		return;
+
+	debugfs_create_file("fw_version", 0444, debugfs, client, &acbel_debugfs_ops);
+}
+
 static const struct i2c_device_id acbel_fsg032_id[] = {
 	{ "acbel_fsg032" },
 	{}
@@ -59,6 +96,7 @@ static int acbel_fsg032_probe(struct i2c_client *client)
 	if (rc)
 		return rc;
 
+	acbel_fsg032_init_debugfs(client);
 	return 0;
 }