[PATCH 3/6] tpm: Implement tpm_chip_find() for other subsystems to call

[Stefan Berger <stefanb@linux.vnet.ibm.com>]

Implement tpm_chip_find() for other subsystems to find a TPM chip and
get a reference to that chip. Once done with using the chip, the reference
is released using tpm_chip_put().

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
---
 drivers/char/tpm/tpm-chip.c | 27 +++++++++++++++++++++++++++
 include/linux/tpm.h         |  5 +++++
 2 files changed, 32 insertions(+)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index 23b667c730f6..b04064291dab 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -84,6 +84,33 @@ void tpm_put_ops(struct tpm_chip *chip)
 EXPORT_SYMBOL_GPL(tpm_put_ops);
 
 /**
+ * tpm_chip_find() - find a TPM chip and get a reference to it
+ */
+struct tpm_chip *tpm_chip_find(void)
+{
+	struct tpm_chip *chip, *res = NULL;
+	int chip_num = 0;
+	int chip_prev;
+
+	mutex_lock(&idr_lock);
+
+	do {
+		chip_prev = chip_num;
+		chip = idr_get_next(&dev_nums_idr, &chip_num);
+		if (chip) {
+			kref_get(&chip->kref);
+			res = chip;
+			break;
+		}
+	} while (chip_prev != chip_num);
+
+	mutex_unlock(&idr_lock);
+
+	return res;
+}
+EXPORT_SYMBOL_GPL(tpm_chip_find);
+
+/**
  * tpm_chip_find_get() - find and reserve a TPM chip
  * @chip:	a &struct tpm_chip instance, %NULL for the default chip
  *
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index cdb3ecdfc933..f0d1abcaf4af 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -61,6 +61,7 @@ extern int tpm_seal_trusted(struct tpm_chip *chip,
 extern int tpm_unseal_trusted(struct tpm_chip *chip,
 			      struct trusted_key_payload *payload,
 			      struct trusted_key_options *options);
+extern struct tpm_chip *tpm_chip_find(void);
 extern void tpm_chip_put(struct tpm_chip *chip);
 #else
 static inline int tpm_is_tpm2(struct tpm_chip *chip)
@@ -97,6 +98,10 @@ static inline int tpm_unseal_trusted(struct tpm_chip *chip,
 {
 	return -ENODEV;
 }
+static inline struct tpm_chip *tpm_chip_find(void)
+{
+	return NULL;
+}
 static inline void tpm_chip_put(struct tpm_chip *chip)
 {
 }
-- 
2.13.6