tpm: Add a helper for checking hwrng enabled

The same checks are repeated in three places to decide whether to use
hwrng.  Consolidate these into a helper.

Also this fixes a case that one of them was missing a check in the
cleanup path.

Fixes: 554b841 ("tpm: Disable RNG for all AMD fTPMs")
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: superm1

drivers/char/tpm/tpm-chip.c

@@ -521,10 +521,20 @@ static int tpm_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 	return tpm_get_random(chip, data, max);
 }
 
+static bool tpm_is_hwrng_enabled(struct tpm_chip *chip)
+{
+	if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM))
+		return false;
+	if (tpm_is_firmware_upgrade(chip))
+		return false;
+	if (chip->flags & TPM_CHIP_FLAG_HWRNG_DISABLED)
+		return false;
+	return true;
+}
+
 static int tpm_add_hwrng(struct tpm_chip *chip)
 {
-	if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM) || tpm_is_firmware_upgrade(chip) ||
-	    chip->flags & TPM_CHIP_FLAG_HWRNG_DISABLED)
+	if (!tpm_is_hwrng_enabled(chip))
 		return 0;
 
 	snprintf(chip->hwrng_name, sizeof(chip->hwrng_name),
@@ -629,7 +639,7 @@ int tpm_chip_register(struct tpm_chip *chip)
 	return 0;
 
 out_hwrng:
-	if (IS_ENABLED(CONFIG_HW_RANDOM_TPM) && !tpm_is_firmware_upgrade(chip))
+	if (tpm_is_hwrng_enabled(chip))
 		hwrng_unregister(&chip->hwrng);
 out_ppi:
 	tpm_bios_log_teardown(chip);
@@ -654,8 +664,7 @@ EXPORT_SYMBOL_GPL(tpm_chip_register);
 void tpm_chip_unregister(struct tpm_chip *chip)
 {
 	tpm_del_legacy_sysfs(chip);
-	if (IS_ENABLED(CONFIG_HW_RANDOM_TPM) && !tpm_is_firmware_upgrade(chip) &&
-	    !(chip->flags & TPM_CHIP_FLAG_HWRNG_DISABLED))
+	if (tpm_is_hwrng_enabled(chip))
 		hwrng_unregister(&chip->hwrng);
 	tpm_bios_log_teardown(chip);
 	if (chip->flags & TPM_CHIP_FLAG_TPM2 && !tpm_is_firmware_upgrade(chip))