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Date:   Wed, 11 May 2022 18:12:16 +0300
From:   Jarkko Sakkinen <jarkko@kernel.org>
To:     Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@infineon.com>
Cc:     Marten.Lindahl@axis.com, jgg@ziepe.ca,
        johannes.holland@infineon.com, jsnitsel@redhat.com,
        linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org,
        martenli@axis.com, nayna@linux.vnet.ibm.com, peterhuewe@gmx.de
Subject: Re: [PATCH 2/2] tpm: Add Field Upgrade mode support for Infineon
 TPM2 modules
Message-ID: <YnvSULFUC9gADu0z@kernel.org>
References: <YnbL9LwDkY+MHdkK@iki.fi>
 <20220509125018.246093-1-stefan.mahnke-hartmann@infineon.com>
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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 M?rten's patch. I can also add the -ENODATA to the if clause
> below or duplicate the code block (similar to M?rten's). Do you have a better
> suggestion?

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

BR, Jarkko