Re: [PATCH 2/2] tpm: Add Field Upgrade mode support for Infineon TPM2 modules

[Jarkko Sakkinen <jarkko@kernel.org>]

On Mon, May 09, 2022 at 02:50:18PM +0200, Stefan Mahnke-Hartmann wrote:
> On 07.05.22 21:43, Jarkko Sakkinen wrote:
> > On Fri, May 06, 2022 at 02:31:48PM +0200, Stefan Mahnke-Hartmann wrote:
> >> TPM2_GetCapability with a capability that has the property type value
> >> of TPM_PT_TOTAL_COMMANDS returns a zero length list, when an Infineon
> >> TPM2 is in Field Upgrade mode.
> >> Since an Infineon TPM2.0 in Field Upgrade mode returns RC_SUCCESS on
> >> TPM2_Startup, the Field Upgrade mode has to be detected by
> >> TPM2_GetCapability.
> >>
> >> Signed-off-by: Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@infineon.com>
> >> ---
> >>  drivers/char/tpm/tpm2-cmd.c | 6 ++++++
> >>  1 file changed, 6 insertions(+)
> >>
> >> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> >> index e62a644ce26b..659130e2936e 100644
> >> --- a/drivers/char/tpm/tpm2-cmd.c
> >> +++ b/drivers/char/tpm/tpm2-cmd.c
> >> @@ -746,6 +746,12 @@ int tpm2_auto_startup(struct tpm_chip *chip)
> >>  	}
> >>  
> >>  	rc = tpm2_get_cc_attrs_tbl(chip);
> >> +	/*
> >> +	 * Infineon TPM in Field Upgrade mode will return no data for the number
> >> +	 * of supported commands.
> >> +	 */
> >> +	if (rc == -ENODATA)
> >> +		rc = TPM2_RC_UPGRADE;
> >
> > Injecting hardware error codes like this is not considered a great idea.
> 
> Resetting the error code was to avoid code duplication, while following the
> same rationale as Mårten's patch. I can also add the -ENODATA to the if clause
> below or duplicate the code block (similar to Mårten's). Do you have a better
> suggestion?

I'd do that instead. It documents better the conditions.

BR, Jarkko