Re: [PATCH v1 1/1] tpm: tis_i2c: Deassert optional reset line before probing

[Jarkko Sakkinen]

On Thu, Sep 17, 2026 at 02:42:11PM +0200, Stefano Radaelli wrote:
> From: Stefano Radaelli <stefano.r@xxxxxxxxxxxxx>
> 
> The common TPM Device Tree binding already documents resets and
> reset-gpios, but the TIS I2C driver never requests a reset control.
> As a result, an I2C TPM held in reset by board wiring remains
> inaccessible and the first register access during probe fails.
> 
> Request the optional reset control and deassert it before
> communicating with the TPM. This keeps existing boards without a reset
> line unchanged while allowing platforms using resets or reset-gpios to
> release the TPM before probe continues.
> 
> Tested on a Variscite DART-MX95 with an ST33KTPM2XI2C TPM using
> reset-gpios.
> 
> Signed-off-by: Stefano Radaelli <stefano.r@xxxxxxxxxxxxx>
> ---
>  drivers/char/tpm/tpm_tis_i2c.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/char/tpm/tpm_tis_i2c.c b/drivers/char/tpm/tpm_tis_i2c.c
> index d55f30fef00a..cde0b093ed58 100644
> --- a/drivers/char/tpm/tpm_tis_i2c.c
> +++ b/drivers/char/tpm/tpm_tis_i2c.c
> @@ -12,6 +12,7 @@
>  
>  #include <linux/i2c.h>
>  #include <linux/crc-ccitt.h>
> +#include <linux/reset.h>
>  #include "tpm_tis_core.h"
>  
>  /* TPM registers */
> @@ -330,6 +331,7 @@ static const struct tpm_tis_phy_ops tpm_i2c_phy_ops = {
>  static int tpm_tis_i2c_probe(struct i2c_client *dev)
>  {
>  	struct tpm_tis_i2c_phy *phy;
> +	struct reset_control *reset;
>  	const u8 crc_enable = 1;
>  	const u8 locality = 0;
>  	int ret;
> @@ -346,6 +348,16 @@ static int tpm_tis_i2c_probe(struct i2c_client *dev)
>  	set_bit(TPM_TIS_DEFAULT_CANCELLATION, &phy->priv.flags);
>  	phy->i2c_client = 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");
> +
> +	ret = reset_control_deassert(reset);
> +	if (ret)
> +		return dev_err_probe(&dev->dev, ret,
> +				     "failed to deassert reset\n");
> +
>  	/* must precede all communication with the tpm */
>  	ret = tpm_tis_i2c_init_guard_time(phy);
>  	if (ret)
> -- 
> 2.47.3
> 

Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

BR, Jarkko