[PATCH v1 1/1] tpm: tis_i2c: Add reset delays for ST33KTPM2XI2C

[PATCH v1 1/1] tpm: tis_i2c: Add reset delays for ST33KTPM2XI2C

[Stefano Radaelli]

From: Stefano Radaelli <stefano.r@variscite.com>

The optional reset control is deasserted without a delay, and probe then
proceeds directly to the first I2C register access. Since reset-gpio
initializes its line asserted, this provides no guaranteed minimum reset
pulse width or recovery interval before communication starts.

Table 66 of the ST33KTPM-IDevID datasheet specifies a minimum reset pulse
width of 1 ms and up to 50 ms from reset release before the first command.
Choose a 2 ms assertion interval to provide margin above the minimum and
wait 50 ms after deassertion, before initializing the I2C guard times.

Associate these timings with the existing st,st33ktpm2xi2c compatible using
match data. Apply the delays only when a reset control is present. Preserve
the existing deassert-only sequence and the behavior of devices without
timing data or a reset control, without adding Device Tree properties.

Link: https://www.st.com/resource/en/datasheet/st33ktpm-idevid.pdf
Signed-off-by: Stefano Radaelli <stefano.r@variscite.com>
---
 drivers/char/tpm/tpm_tis_i2c.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/char/tpm/tpm_tis_i2c.c b/drivers/char/tpm/tpm_tis_i2c.c
index cde0b093ed58..8bcbc84815fd 100644
--- a/drivers/char/tpm/tpm_tis_i2c.c
+++ b/drivers/char/tpm/tpm_tis_i2c.c
@@ -12,6 +12,8 @@
 
 #include <linux/i2c.h>
 #include <linux/crc-ccitt.h>
+#include <linux/delay.h>
+#include <linux/property.h>
 #include <linux/reset.h>
 #include "tpm_tis_core.h"
 
@@ -55,6 +57,11 @@
 #define TPM_INTF_CAPABILITY_ZERO 0x0FFFF000
 #define TPM_I2C_INTERFACE_CAPABILITY_ZERO 0x80000000
 
+struct tpm_tis_i2c_reset_timings {
+	unsigned int assert_us;
+	unsigned int deassert_us;
+};
+
 struct tpm_tis_i2c_phy {
 	struct tpm_tis_data priv;
 	struct i2c_client *i2c_client;
@@ -330,6 +337,7 @@ static const struct tpm_tis_phy_ops tpm_i2c_phy_ops = {
 
 static int tpm_tis_i2c_probe(struct i2c_client *dev)
 {
+	const struct tpm_tis_i2c_reset_timings *timings;
 	struct tpm_tis_i2c_phy *phy;
 	struct reset_control *reset;
 	const u8 crc_enable = 1;
@@ -347,17 +355,25 @@ static int tpm_tis_i2c_probe(struct i2c_client *dev)
 
 	set_bit(TPM_TIS_DEFAULT_CANCELLATION, &phy->priv.flags);
 	phy->i2c_client = dev;
+	timings = device_get_match_data(&dev->dev);
 
 	reset = devm_reset_control_get_optional_exclusive(&dev->dev, NULL);
 	if (IS_ERR(reset))
 		return dev_err_probe(&dev->dev, PTR_ERR(reset),
 				     "failed to get reset control\n");
 
+	/* Allow an already asserted reset to meet its minimum pulse width. */
+	if (reset && timings)
+		fsleep(timings->assert_us);
+
 	ret = reset_control_deassert(reset);
 	if (ret)
 		return dev_err_probe(&dev->dev, ret,
 				     "failed to deassert reset\n");
 
+	if (reset && timings)
+		fsleep(timings->deassert_us);
+
 	/* must precede all communication with the tpm */
 	ret = tpm_tis_i2c_init_guard_time(phy);
 	if (ret)
@@ -393,9 +409,19 @@ static const struct i2c_device_id tpm_tis_i2c_id[] = {
 MODULE_DEVICE_TABLE(i2c, tpm_tis_i2c_id);
 
 #ifdef CONFIG_OF
+/*
+ * ST33KTPM-IDevID datasheet DS15011, table 66: tWL >= 1 ms and
+ * tCMD <= 50 ms. Allow 2 ms for tWL to provide margin above the minimum.
+ */
+static const struct tpm_tis_i2c_reset_timings st33ktpm2xi2c_reset_timings = {
+	.assert_us = 2000,
+	.deassert_us = 50000,
+};
+
 static const struct of_device_id of_tis_i2c_match[] = {
 	{ .compatible = "infineon,slb9673", },
 	{ .compatible = "nuvoton,npct75x", },
+	{ .compatible = "st,st33ktpm2xi2c", .data = &st33ktpm2xi2c_reset_timings },
 	{ .compatible = "tcg,tpm-tis-i2c", },
 	{}
 };
-- 
2.47.3

Re: [PATCH v1 1/1] tpm: tis_i2c: Add reset delays for ST33KTPM2XI2C

[Jarkko Sakkinen]

On Wed, Oct 28, 2026 at 10:45:04AM +0100, Stefano Radaelli wrote:
> From: Stefano Radaelli <stefano.r@variscite.com>
> 
> The optional reset control is deasserted without a delay, and probe then
> proceeds directly to the first I2C register access. Since reset-gpio
> initializes its line asserted, this provides no guaranteed minimum reset
> pulse width or recovery interval before communication starts.
> 
> Table 66 of the ST33KTPM-IDevID datasheet specifies a minimum reset pulse
> width of 1 ms and up to 50 ms from reset release before the first command.
> Choose a 2 ms assertion interval to provide margin above the minimum and
> wait 50 ms after deassertion, before initializing the I2C guard times.
> 
> Associate these timings with the existing st,st33ktpm2xi2c compatible using
> match data. Apply the delays only when a reset control is present. Preserve
> the existing deassert-only sequence and the behavior of devices without
> timing data or a reset control, without adding Device Tree properties.

"Pull the timings from the matched device entry. If they don't exist,
fall back to the legacy behavior without delays. Update of_tis_i2c_match
with the timings for st33ktpm2xi2c."

I.e. the last paragraph has the language of a white paper.

Br, Jarkko

Re: [PATCH v1 1/1] tpm: tis_i2c: Add reset delays for ST33KTPM2XI2C

[Stefano Radaelli]

On Wed, Oct 28, 2026 at 10:32:49PM +0200, Jarkko Sakkinen wrote:
> 
> "Pull the timings from the matched device entry. If they don't exist,
> fall back to the legacy behavior without delays. Update of_tis_i2c_match
> with the timings for st33ktpm2xi2c."
> 
> I.e. the last paragraph has the language of a white paper.
> 

Hi Jarkko,

thank you for the review, I'm sending the v2.

Best Regards,
Stefano