[PATCH v2] tpm: tpm_tis: Add optional delay after relinquish

[Jim Broadus <jbroadus@gmail.com>]

Some TPMs fail to grant locality when requested immediately after being
relinquished. In this case, the TPM_ACCESS_REQUEST_USE bit of the
TPM_ACCESS register is cleared immediately without setting
TPM_ACCESS_ACTIVE_LOCALITY.

This issue can be seen at boot since tpm_chip_start, called right
after locality is relinquished, fails. This causes the probe to fail:

tpm_tis MSFT0101:00: probe with driver tpm_tis failed with error -1

This occurs on some older Dell Latitudes and maybe others. To work
around this, add a "settle" boolean param to tpm_tis. When this is
enabled, a delay is added after locality is relinquished.

Signed-off-by: Jim Broadus <jbroadus@gmail.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 7 +++++++
 drivers/char/tpm/tpm_tis.c                      | 7 +++++++
 drivers/char/tpm/tpm_tis_core.c                 | 3 +++
 drivers/char/tpm/tpm_tis_core.h                 | 1 +
 4 files changed, 18 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 4d0f545fb3ec..5b7111033fbb 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -7651,6 +7651,13 @@ Kernel parameters
 			defined by Trusted Computing Group (TCG) see
 			https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/
 
+	tpm_tis.settle= [HW,TPM]
+			Format: <bool>
+			When enabled, this adds a delay after locality is
+			relinquished. Some TPMs will fail to grant locality if
+			requested immediately after being relinquished. This
+			causes the probe to fail.
+
 	tp_printk	[FTRACE]
 			Have the tracepoints sent to printk as well as the
 			tracing ring buffer. This is useful for early boot up
diff --git a/drivers/char/tpm/tpm_tis.c b/drivers/char/tpm/tpm_tis.c
index 9aa230a63616..8ac0ea78570e 100644
--- a/drivers/char/tpm/tpm_tis.c
+++ b/drivers/char/tpm/tpm_tis.c
@@ -101,6 +101,10 @@ module_param(force, bool, 0444);
 MODULE_PARM_DESC(force, "Force device probe rather than using ACPI entry");
 #endif
 
+static bool settle;
+module_param(settle, bool, 0444);
+MODULE_PARM_DESC(settle, "Add settle time after relinquish");
+
 #if defined(CONFIG_PNP) && defined(CONFIG_ACPI)
 static int has_hid(struct acpi_device *dev, const char *hid)
 {
@@ -242,6 +246,9 @@ static int tpm_tis_init(struct device *dev, struct tpm_info *tpm_info)
 	if (itpm || is_itpm(ACPI_COMPANION(dev)))
 		set_bit(TPM_TIS_ITPM_WORKAROUND, &phy->priv.flags);
 
+	if (settle)
+		set_bit(TPM_TIS_SETTLE_AFTER_RELINQUISH, &phy->priv.flags);
+
 	return tpm_tis_core_init(dev, &phy->priv, irq, &tpm_tcg,
 				 ACPI_HANDLE(dev));
 }
diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 21d79ad3b164..fbeee085098e 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -171,6 +171,9 @@ static int __tpm_tis_relinquish_locality(struct tpm_tis_data *priv, int l)
 {
 	tpm_tis_write8(priv, TPM_ACCESS(l), TPM_ACCESS_ACTIVE_LOCALITY);
 
+	if (test_bit(TPM_TIS_SETTLE_AFTER_RELINQUISH, &priv->flags))
+		tpm_msleep(TPM_TIMEOUT);
+
 	return 0;
 }
 
diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
index 6c3aa480396b..413cac5e0f31 100644
--- a/drivers/char/tpm/tpm_tis_core.h
+++ b/drivers/char/tpm/tpm_tis_core.h
@@ -90,6 +90,7 @@ enum tpm_tis_flags {
 	TPM_TIS_DEFAULT_CANCELLATION	= 2,
 	TPM_TIS_IRQ_TESTED		= 3,
 	TPM_TIS_STATUS_VALID_RETRY	= 4,
+	TPM_TIS_SETTLE_AFTER_RELINQUISH	= 5,
 };
 
 struct tpm_tis_data {
-- 
2.54.0