[PATCH v2 1/1] tpm: tis_i2c: Add reset delays for ST33KTPM2XI2C

[PATCH v2 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.

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.

Link: https://www.st.com/resource/en/datasheet/st33ktpm-idevid.pdf
Signed-off-by: Stefano Radaelli <stefano.r@variscite.com>
---
v1->v2:
 - Rewrite the last paragraph of the commit message

 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 v2 1/1] tpm: tis_i2c: Add reset delays for ST33KTPM2XI2C

[Jarkko Sakkinen]

On Thu, Oct 29, 2026 at 10:55:28AM +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.
> 
> 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.
> 
> Link: https://www.st.com/resource/en/datasheet/st33ktpm-idevid.pdf
> Signed-off-by: Stefano Radaelli <stefano.r@variscite.com>
> ---
> v1->v2:
>  - Rewrite the last paragraph of the commit message
> 
>  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
> 

Thanks, LGTM.


Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

Br, Jarkko