Re: [RFC v2 2/5] tpm_crb: Add new wrapper function to invoke start method

[Jarkko Sakkinen <jarkko@kernel.org>]

On Tue, Mar 24, 2026 at 11:42:41PM +0530, Arun Menon wrote:
> The current implementation handles different platform start methods
> (ACPI, ARM SMC, and ARM FFA) directly within crb_send(), but it is
> limited to triggering the CRB_START_INVOKE bit.
> 
> To support cmd/rsp chunking, the driver must be able to send other
> control bits, like CRB_START_NEXT_CHUNK, using these same
> platform-specific paths.
> 
> By moving this logic into a new helper function, crb_trigger_tpm(),
> the driver can now send any required control bit across all supported
> platforms. This prepares the driver for the upcoming chunking support.
> 
> No functional change is intended.
> 
> Signed-off-by: Arun Menon <armenon@redhat.com>
> ---
>  drivers/char/tpm/tpm_crb.c | 50 ++++++++++++++++++++------------------
>  1 file changed, 27 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c
> index 67c0061d4cab7..922bcf7a69ad5 100644
> --- a/drivers/char/tpm/tpm_crb.c
> +++ b/drivers/char/tpm/tpm_crb.c
> @@ -445,6 +445,32 @@ static int tpm_crb_smc_start(struct device *dev, unsigned long func_id)
>  }
>  #endif
>  
> +static int crb_trigger_tpm(struct tpm_chip *chip, u32 start_cmd)

tpm_crb_start?

I'd also split this into two commits:

1. One that splits the helper.
2. Second that adds the new stuff.

> +{
> +	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
> +	int rc = 0;
> +	/* The reason for the extra quirk is that the PTT in 4th Gen Core CPUs
> +	 * report only ACPI start but in practice seems to require both
> +	 * CRB start, hence invoking CRB start method if hid == MSFT0101.
> +	 */
> +	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER ||
> +	    priv->sm == ACPI_TPM2_MEMORY_MAPPED ||
> +	    !strcmp(priv->hid, "MSFT0101"))
> +		iowrite32(start_cmd, &priv->regs_t->ctrl_start);
> +	if (priv->sm == ACPI_TPM2_START_METHOD ||
> +	    priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_START_METHOD)
> +		rc = crb_do_acpi_start(chip);
> +	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_ARM_SMC) {
> +		iowrite32(start_cmd, &priv->regs_t->ctrl_start);
> +		rc = tpm_crb_smc_start(&chip->dev, priv->smc_func_id);
> +	}
> +	if (priv->sm == ACPI_TPM2_CRB_WITH_ARM_FFA) {
> +		iowrite32(start_cmd, &priv->regs_t->ctrl_start);
> +		rc = tpm_crb_ffa_start(CRB_FFA_START_TYPE_COMMAND, chip->locality);
> +	}
> +	return rc;
> +}
> +
>  static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len)
>  {
>  	struct crb_priv *priv = dev_get_drvdata(&chip->dev);
> @@ -470,29 +496,7 @@ static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len)
>  	/* Make sure that cmd is populated before issuing start. */
>  	wmb();
>  
> -	/* The reason for the extra quirk is that the PTT in 4th Gen Core CPUs
> -	 * report only ACPI start but in practice seems to require both
> -	 * CRB start, hence invoking CRB start method if hid == MSFT0101.
> -	 */
> -	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER ||
> -	    priv->sm == ACPI_TPM2_MEMORY_MAPPED ||
> -	    !strcmp(priv->hid, "MSFT0101"))
> -		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
> -
> -	if (priv->sm == ACPI_TPM2_START_METHOD ||
> -	    priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_START_METHOD)
> -		rc = crb_do_acpi_start(chip);
> -
> -	if (priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_ARM_SMC) {
> -		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
> -		rc = tpm_crb_smc_start(&chip->dev, priv->smc_func_id);
> -	}
> -
> -	if (priv->sm == ACPI_TPM2_CRB_WITH_ARM_FFA) {
> -		iowrite32(CRB_START_INVOKE, &priv->regs_t->ctrl_start);
> -		rc = tpm_crb_ffa_start(CRB_FFA_START_TYPE_COMMAND, chip->locality);
> -	}
> -
> +	rc = crb_trigger_tpm(chip, CRB_START_INVOKE);
>  	if (rc)
>  		return rc;
>  
> -- 
> 2.53.0
> 

BR, Jarkko