Re: [PATCH] tpm: tpm_tis: Add optional delay after relinquish

[Jim Broadus]

I realize the delay should be moved to __tpm_tis_relinquish_locality.
I'll change that in a v2 patch.


On Mon, May 18, 2026 at 11:09 PM Jim Broadus <jbroadus@xxxxxxxxx> wrote:
>
> Some TPMs fail to grant locality when requested immediately after being
> relinquished. In this case, the TPM_ACCESS_REQUEST_USE bit of the
> TPM_ACCESS register is cleared immediately without setting
> TPM_ACCESS_ACTIVE_LOCALITY.
>
> This issue can be seen at boot since tpm_chip_start, called right
> after locality is relinquished, fails. This causes the probe to fail:
>
> tpm_tis MSFT0101:00: probe with driver tpm_tis failed with error -1
>
> This occurs on some older Dell Latitudes and maybe others. To work
> around this, add a "settle" boolean param to tpm_tis. When this is
> enabled, a delay is added after locality is relinquished.
>
> Signed-off-by: Jim Broadus <jbroadus@xxxxxxxxx>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 7 +++++++
>  drivers/char/tpm/tpm_tis.c                      | 7 +++++++
>  drivers/char/tpm/tpm_tis_core.c                 | 3 +++
>  drivers/char/tpm/tpm_tis_core.h                 | 1 +
>  4 files changed, 18 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 4d0f545fb3ec..5b7111033fbb 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -7651,6 +7651,13 @@ Kernel parameters
>                         defined by Trusted Computing Group (TCG) see
>                         https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/
>
> +       tpm_tis.settle= [HW,TPM]
> +                       Format: <bool>
> +                       When enabled, this adds a delay after locality is
> +                       relinquished. Some TPMs will fail to grant locality if
> +                       requested immediately after being relinquished. This
> +                       causes the probe to fail.
> +
>         tp_printk       [FTRACE]
>                         Have the tracepoints sent to printk as well as the
>                         tracing ring buffer. This is useful for early boot up
> diff --git a/drivers/char/tpm/tpm_tis.c b/drivers/char/tpm/tpm_tis.c
> index 9aa230a63616..8ac0ea78570e 100644
> --- a/drivers/char/tpm/tpm_tis.c
> +++ b/drivers/char/tpm/tpm_tis.c
> @@ -101,6 +101,10 @@ module_param(force, bool, 0444);
>  MODULE_PARM_DESC(force, "Force device probe rather than using ACPI entry");
>  #endif
>
> +static bool settle;
> +module_param(settle, bool, 0444);
> +MODULE_PARM_DESC(settle, "Add settle time after relinquish");
> +
>  #if defined(CONFIG_PNP) && defined(CONFIG_ACPI)
>  static int has_hid(struct acpi_device *dev, const char *hid)
>  {
> @@ -242,6 +246,9 @@ static int tpm_tis_init(struct device *dev, struct tpm_info *tpm_info)
>         if (itpm || is_itpm(ACPI_COMPANION(dev)))
>                 set_bit(TPM_TIS_ITPM_WORKAROUND, &phy->priv.flags);
>
> +       if (settle)
> +               set_bit(TPM_TIS_SETTLE_AFTER_RELINQUISH, &phy->priv.flags);
> +
>         return tpm_tis_core_init(dev, &phy->priv, irq, &tpm_tcg,
>                                  ACPI_HANDLE(dev));
>  }
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index 21d79ad3b164..68be26fa5817 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -184,6 +184,9 @@ static int tpm_tis_relinquish_locality(struct tpm_chip *chip, int l)
>                 __tpm_tis_relinquish_locality(priv, l);
>         mutex_unlock(&priv->locality_count_mutex);
>
> +       if (test_bit(TPM_TIS_SETTLE_AFTER_RELINQUISH, &priv->flags))
> +               tpm_msleep(TPM_TIMEOUT);
> +
>         return 0;
>  }
>
> diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
> index 6c3aa480396b..413cac5e0f31 100644
> --- a/drivers/char/tpm/tpm_tis_core.h
> +++ b/drivers/char/tpm/tpm_tis_core.h
> @@ -90,6 +90,7 @@ enum tpm_tis_flags {
>         TPM_TIS_DEFAULT_CANCELLATION    = 2,
>         TPM_TIS_IRQ_TESTED              = 3,
>         TPM_TIS_STATUS_VALID_RETRY      = 4,
> +       TPM_TIS_SETTLE_AFTER_RELINQUISH = 5,
>  };
>
>  struct tpm_tis_data {
> --
> 2.54.0
>