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

[Jarkko Sakkinen <jarkko@kernel.org>]

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