tpm: Use container_of to locate the tpm_chip in tpm_open

misc_open sets the file->private_date to the misc_dev when calling
open. We can use container_of to go from the misc_dev back to the
tpm_chip.

Future clean ups will move tpm_open into a new file and this change
means we do not have to export the tpm_chip list.

Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Reviewed-by: Joel Schopp <jschopp@linux.vnet.ibm.com>
Reviewed-by: Peter Huewe <peterhuewe@gmx.de>
Acked-by: Ashley Lai <adlai@linux.vnet.ibm.com>
Signed-off-by: Peter Huewe <peterhuewe@gmx.de>

drivers/char/tpm/tpm.c

@@ -1170,38 +1170,25 @@ EXPORT_SYMBOL_GPL(wait_for_tpm_stat);
  */
 int tpm_open(struct inode *inode, struct file *file)
 {
-	int minor = iminor(inode);
-	struct tpm_chip *chip = NULL, *pos;
-
-	rcu_read_lock();
-	list_for_each_entry_rcu(pos, &tpm_chip_list, list) {
-		if (pos->vendor.miscdev.minor == minor) {
-			chip = pos;
-			get_device(chip->dev);
-			break;
-		}
-	}
-	rcu_read_unlock();
-
-	if (!chip)
-		return -ENODEV;
+	struct miscdevice *misc = file->private_data;
+	struct tpm_chip *chip = container_of(misc, struct tpm_chip,
+					     vendor.miscdev);
 
 	if (test_and_set_bit(0, &chip->is_open)) {
 		dev_dbg(chip->dev, "Another process owns this TPM\n");
-		put_device(chip->dev);
 		return -EBUSY;
 	}
 
 	chip->data_buffer = kzalloc(TPM_BUFSIZE, GFP_KERNEL);
 	if (chip->data_buffer == NULL) {
 		clear_bit(0, &chip->is_open);
-		put_device(chip->dev);
 		return -ENOMEM;
 	}
 
 	atomic_set(&chip->data_pending, 0);
 
 	file->private_data = chip;
+	get_device(chip->dev);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(tpm_open);