CHROMIUM: workaround for Infineon TPM defensive timeout (v2)

The SLB9635 TPM by Infineon goes into a self-defense mode when
power is cut in the middle of a command too many times, and getting
it out of that mode is difficult and takes a long time.  This patch
adds a shutdown-time callback that grabs the mutex wrapping a
request-response transaction, so it's less likely that we'll lose
power in the middle of a command.

Note that the TPM may lose power also across suspend/resume (depending
on hardware).  However, the suspend callback sends a SaveState command,
which can only be sent when other running commands have completed.
I am not sure if a command can start after the suspend callback
has completed (I doubt it) but even if it does, it will be
a sufficiently rare event, and the self-defense can tolerate that.

The "gentle shutdown" message is added to make it easier to detect
if we neglect to carry this patch forward.

BUG=chromium:234796
TEST=extensively tested with the librarian simulator
Signed-off-by: Luigi Semenzato <[email protected]>

Change-Id: I1bb0a6d574c96a33f4344d47e3e7584e3f67fb14
Reviewed-on: https://gerrit.chromium.org/gerrit/58902
Tested-by: Luigi Semenzato <[email protected]>
Reviewed-by: Darren Krahn <[email protected]>
Commit-Queue: Luigi Semenzato <[email protected]>
Reviewed-by: Olof Johansson <[email protected]>

Author: Luigi Semenzato

drivers/char/tpm/tpm.c

@@ -29,6 +29,7 @@
 #include <linux/mutex.h>
 #include <linux/spinlock.h>
 #include <linux/freezer.h>
+#include <linux/reboot.h>
 
 #include "tpm.h"
 #include "tpm_eventlog.h"
@@ -1465,10 +1466,22 @@ static void tpm_dev_release(struct device *dev)
 	tpm_dev_vendor_release(chip);
 
 	chip->release(dev);
+	unregister_reboot_notifier(&chip->shutdown_nb);
 	kfree(chip);
 }
 EXPORT_SYMBOL_GPL(tpm_dev_release);
 
+static int tpm_shutdown_notify(struct notifier_block *nb,
+				unsigned long unused, void *unused2)
+{
+	struct tpm_chip *chip = container_of(nb, struct tpm_chip, shutdown_nb);
+	dev_dbg(chip->dev, "acquiring shutdown lock\n");
+	mutex_lock(&chip->tpm_mutex);
+	dev_dbg(chip->dev, "acquired shutdown lock\n");
+	return NOTIFY_DONE;
+}
+
+
 /*
  * Called from tpm_<specific>.c probe function only for devices 
  * the driver has determined it should claim.  Prior to calling
@@ -1549,6 +1562,13 @@ struct tpm_chip *tpm_register_hardware(struct device *dev,
 	list_add_rcu(&chip->list, &tpm_chip_list);
 	spin_unlock(&driver_lock);
 
+	/* INFINEON TPM WORKAROUND: Register shutdown callback that ensures we
+	 * don't shut down in the middle of a TPM command, or we may trigger
+	 * nasty defensive timeouts at the next boot.
+	 */
+	chip->shutdown_nb.notifier_call = tpm_shutdown_notify;
+	register_reboot_notifier(&chip->shutdown_nb);
+
 	return chip;
 
 put_device:

drivers/char/tpm/tpm.h

@@ -133,6 +133,7 @@ struct tpm_chip {
 
 	struct list_head list;
 	void (*release) (struct device *);
+	struct notifier_block shutdown_nb;
 };
 
 #define to_tpm_chip(n) container_of(n, struct tpm_chip, vendor)

drivers/char/tpm/tpm_tis.c

@@ -536,7 +536,7 @@ static int tpm_tis_init(struct device *dev, resource_size_t start,
 	vendor = ioread32(chip->vendor.iobase + TPM_DID_VID(0));
 
 	dev_info(dev,
-		 "1.2 TPM (device-id 0x%X, rev-id %d)\n",
+		 "1.2 TPM (device-id 0x%X, rev-id %d) [gentle shutdown]\n",
 		 vendor >> 16, ioread8(chip->vendor.iobase + TPM_RID(0)));
 
 	if (!itpm) {