tpm: suppress durations sysfs output if not set

Suppress the output of durations if they were not read during driver initialization.
This is similar to other sysfs entries that return nothing if for some reason sending the commands to the TPM fails.

Signed-off-by Stefan Berger <[email protected]>

---
 drivers/char/tpm/tpm.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux-2.6/drivers/char/tpm/tpm.c
===================================================================

drivers/char/tpm/tpm.c +3 -0

@@ -963,6 +963,9 @@ ssize_t tpm_show_durations(struct device
 {
     struct tpm_chip *chip = dev_get_drvdata(dev);
 
+    if (chip->vendor.duration[TPM_LONG] == 0)
+        return 0;
+
     return sprintf(buf, "%d %d %d [%s]\n",
                jiffies_to_usecs(chip->vendor.duration[TPM_SHORT]),
                jiffies_to_usecs(chip->vendor.duration[TPM_MEDIUM]),