[PATCH v3] tpm: Add version_major sysfs file

[Jerry Snitselaar <jsnitsel@redhat.com>]

Easily determining what TCG version a tpm device implements
has been a pain point for userspace for a long time, so
add a sysfs file to report the TCG version of a tpm device.

Also add an entry to Documentation/ABI/stable/sysfs-class-tpm
describing the new file.

Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: Peter Huewe <peterhuewe@gmx.de>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: linux-integrity@vger.kernel.org
Signed-off-by: Jerry Snitselaar <jsnitsel@redhat.com>
---
v3: - Change file name to version_major.
v2: - Fix TCG usage in commit message.
    - Add entry to sysfs-class-tpm in Documentation/ABI/stable

 Documentation/ABI/stable/sysfs-class-tpm | 11 ++++++++
 drivers/char/tpm/tpm-sysfs.c             | 34 +++++++++++++++++++-----
 2 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/Documentation/ABI/stable/sysfs-class-tpm b/Documentation/ABI/stable/sysfs-class-tpm
index c0e23830f56a..116f8d3a8ddc 100644
--- a/Documentation/ABI/stable/sysfs-class-tpm
+++ b/Documentation/ABI/stable/sysfs-class-tpm
@@ -183,3 +183,14 @@ Description:	The "timeouts" property shows the 4 vendor-specific values
 		The four timeout values are shown in usecs, with a trailing
 		"[original]" or "[adjusted]" depending on whether the values
 		were scaled by the driver to be reported in usec from msecs.
+
+What:		/sys/class/tpm/tpmX/version_major
+Date:		October 2019
+KernelVersion:	5.5
+Contact:	linux-integrity@vger.kernel.org
+Description:	The "version_major" property shows the TCG spec version
+		implemented by the TPM device.
+
+		Example output:
+
+		2.0
diff --git a/drivers/char/tpm/tpm-sysfs.c b/drivers/char/tpm/tpm-sysfs.c
index edfa89160010..6993ef00f256 100644
--- a/drivers/char/tpm/tpm-sysfs.c
+++ b/drivers/char/tpm/tpm-sysfs.c
@@ -309,7 +309,17 @@ static ssize_t timeouts_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RO(timeouts);
 
-static struct attribute *tpm_dev_attrs[] = {
+static ssize_t version_major_show(struct device *dev,
+				  struct device_attribute *attr, char *buf)
+{
+	struct tpm_chip *chip = to_tpm_chip(dev);
+
+	return sprintf(buf, "%s\n", chip->flags & TPM_CHIP_FLAG_TPM2
+		       ? "2.0" : "1.2");
+}
+static DEVICE_ATTR_RO(version_major);
+
+static struct attribute *tpm12_dev_attrs[] = {
 	&dev_attr_pubek.attr,
 	&dev_attr_pcrs.attr,
 	&dev_attr_enabled.attr,
@@ -320,18 +330,28 @@ static struct attribute *tpm_dev_attrs[] = {
 	&dev_attr_cancel.attr,
 	&dev_attr_durations.attr,
 	&dev_attr_timeouts.attr,
+	&dev_attr_version_major.attr,
 	NULL,
 };
 
-static const struct attribute_group tpm_dev_group = {
-	.attrs = tpm_dev_attrs,
+static struct attribute *tpm20_dev_attrs[] = {
+	&dev_attr_version_major.attr,
+	NULL
+};
+
+static const struct attribute_group tpm12_dev_group = {
+	.attrs = tpm12_dev_attrs,
+};
+
+static const struct attribute_group tpm20_dev_group = {
+	.attrs = tpm20_dev_attrs,
 };
 
 void tpm_sysfs_add_device(struct tpm_chip *chip)
 {
-	if (chip->flags & TPM_CHIP_FLAG_TPM2)
-		return;
-
 	WARN_ON(chip->groups_cnt != 0);
-	chip->groups[chip->groups_cnt++] = &tpm_dev_group;
+	if (chip->flags & TPM_CHIP_FLAG_TPM2)
+		chip->groups[chip->groups_cnt++] = &tpm20_dev_group;
+	else
+		chip->groups[chip->groups_cnt++] = &tpm12_dev_group;
 }
-- 
2.23.0