linux-kernel - Re: [PATCH] tpm: Add sysfs interface to show TPM hardware version

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Date:   Mon, 13 Mar 2017 08:10:53 +0100
From:   Peter Huewe <peterhuewe@....de>
To:     Meng.Li@...driver.com, linux-kernel@...r.kernel.org
CC:     tpmdd@...horst.net, jarkko.sakkinen@...ux.intel.com,
        jgunthorpe@...idianresearch.com, tpmdd-devel@...ts.sourceforge.net
Subject: Re: [PATCH] tpm: Add sysfs interface to show TPM hardware version

Hi,
Thanks for your patch.

Am 13. März 2017 06:21:57 MEZ schrieb Meng.Li@...driver.com:
>From: Limeng <Meng.Li@...driver.com>
>
>So far, there is not a sysfs interface for user space code to
>check the TPM hardware version(TPM1.x or TPM2). So, add a
>file named description in /sys/class/tpm/tpmX/ to show it.
It's not really the hardware version but the "TPM Family" according to tcg.

And yes you are right there is currently no way, except for trial and error, for the userspace to determine this.
So an interface to get this information makes sense to me.
>
>Signed-off-by: Meng Li <Meng.Li@...driver.com>
>---
>drivers/char/tpm/tpm-chip.c |   85
>+++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 85 insertions(+)
>
>diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
>index c406343..da2cd69 100644
>--- a/drivers/char/tpm/tpm-chip.c
>+++ b/drivers/char/tpm/tpm-chip.c
>@@ -36,6 +36,83 @@
> dev_t tpm_devt;
> 
> /**
>+ * show_description - sysfs interface for checking current TPM
>hardware version.
>+ * @dev:	pointer to tpm chip device
>+ * @attr:	unused
>+ * @buf:	char buffer to be filled with TPM hardware version info
>+ *
>+ * Provides sysfs interface for showing current TPM hardware version.
>+ */
>+static ssize_t show_description(struct device *dev,
>+		struct device_attribute *attr, char *buf)
>+{
>+	struct tpm_chip *chip = (struct tpm_chip *)container_of(dev,struct
>tpm_chip,dev);
>+	int ret;
>+
>+	if (chip->flags & TPM_CHIP_FLAG_TPM2)
>+		ret = sprintf(buf, "TPM 2.0");
>+	else
>+		ret = sprintf(buf, "TPM 1.x");
>+
>+	return ret;
>+}
>+
>+/**
>+ * store_description - interface for manually setting data.
>+ * @dev:	unused
>+ * @attr:	unused
>+ * @buf:	unused
>+ * @count:	unused
>+ *
>+ * There is not any process in this function, reserve for feature.
>+ */
>+static ssize_t store_description(struct device *dev, struct
>device_attribute *attr,
>+		const char *buf, size_t count)
>+{
>+	return count;
>+}
Since it does not do anything
I would not create this function and leave the sysfs node as S_IRUGO.

>+
>+static struct device_attribute tpm_attrs[] = {
>+	__ATTR(description, S_IRUGO | S_IWUSR, show_description,
>store_description),
>+};
>+
>+/**
>+ * tpm_create_sysfs - Create tpm sysfs interface.
>+ * @dev:	pointer to tpm chip device
>+ *
>+ * Create sysfs interface for checking current TPM hardware version.
>+ */
>+static int tpm_create_sysfs(struct device *dev)
>+{
>+	int r, t;
>+
>+	for (t = 0; t < ARRAY_SIZE(tpm_attrs); t++) {
>+		r = device_create_file(dev, &tpm_attrs[t]);
>+		if (r) {
>+			dev_err(dev, "failed to create sysfs file\n");
>+			return r;
>+		}
>+	}
>+
>+	return 0;
>+}
>+
>+/**
>+ * tpm_remove_sysfs - Remove tpm sysfs interface.
>+ * @dev:	pointer to tpm chip device
>+ *
>+ * Remove sysfs interface for checking current TPM hardware version.
>+ */
>+static void tpm_remove_sysfs(struct device *dev)
>+{
>+	int  t;
>+
>+	for (t = 0; t < ARRAY_SIZE(tpm_attrs); t++) {
>+		device_remove_file(dev, &tpm_attrs[t]);
>+	}
>+}
>+
>+/**
>  * tpm_try_get_ops() - Get a ref to the tpm_chip
>  * @chip: Chip to ref
>  *
>@@ -363,6 +440,13 @@ int tpm_chip_register(struct tpm_chip *chip)
> 		return rc;
> 	}
> 
>+	rc = tpm_create_sysfs(&chip->dev);
>+	if (rc) {
>+		tpm_del_legacy_sysfs(chip);
>+		tpm_chip_unregister(chip);
>+		return rc;
>+	}
>+
> 	return 0;
> }
> EXPORT_SYMBOL_GPL(tpm_chip_register);
>@@ -382,6 +466,7 @@ int tpm_chip_register(struct tpm_chip *chip)
>  */
> void tpm_chip_unregister(struct tpm_chip *chip)
> {
>+	tpm_remove_sysfs(&chip->dev);
> 	tpm_del_legacy_sysfs(chip);
> 	tpm_bios_log_teardown(chip);
> 	tpm_del_char_device(chip);

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