linux-kernel - Re: [PATCH v9 2/8] tpm: tpm_tis: Fix expected bit handling and send all bytes in one shot without last byte in exception

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Date:   Mon, 1 Jun 2020 05:30:47 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     amirmizi6@...il.com
Cc:     Eyal.Cohen@...oton.com, oshrialkoby85@...il.com,
        alexander.steffen@...ineon.com, robh+dt@...nel.org,
        peterhuewe@....de, christophe-h.richard@...com, jgg@...pe.ca,
        arnd@...db.de, gregkh@...uxfoundation.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-integrity@...r.kernel.org, oshri.alkoby@...oton.com,
        tmaimon77@...il.com, gcwilson@...ibm.com, kgoldman@...ibm.com,
        Dan.Morav@...oton.com, oren.tanami@...oton.com,
        shmulik.hager@...oton.com, amir.mizinski@...oton.com,
        Benoit Houyere <benoit.houyere@...com>
Subject: Re: [PATCH v9 2/8] tpm: tpm_tis: Fix expected bit handling and send
 all bytes in one shot without last byte in exception

On Tue, May 26, 2020 at 05:16:52PM +0300, amirmizi6@...il.com wrote:
> From: Amir Mizinski <amirmizi6@...il.com>
> 
> Incorrect implementation of send message was detected. We polled only
> TPM_STS.stsValid bit and then we single-checked the TPM_STS.expect bit
> value.
> TPM_STS.expected bit should be checked at the same time as
> TPM_STS.stsValid bit, and this should be repeated until timeout_A.

I don't understand what the first paragraph is trying to say. It does
not conclude to anything. Please write instead soemthing that explains
what is going on.

> To detect a TPM_STS.expected bit reset, the "wait_for_tpm_stat" function is
> modified to "wait_for_tpm_stat_result". This function regularly reads the
> status register and check the bits defined by "mask" to reach the value
> defined in "mask_result".

Please remove this and explain instead how are you are changing the
existing function.

> This correct implementation is required for using the new CRC calculation
> on I2C TPM command bytes or I2C TPM answer bytes. TPM_STS.expected bit is
> reset after all bytes are acquired and the CRC result is inserted in the
> dedicated register. It introduces a normal latency for TPM_STS.expected
> bit reset.
> 
> Respectively, to send a message, as defined in
> TCG_DesignPrinciples_TPM2p0Driver_vp24_pubrev.pdf, all bytes should be
> sent in one shot instead of sending the last byte separately.
> 
> Suggested-by: Benoit Houyere <benoit.houyere@...com>
> Signed-off-by: Amir Mizinski <amirmizi6@...il.com>
> ---
>  drivers/char/tpm/tpm_tis_core.c | 74 +++++++++++++++++------------------------
>  1 file changed, 30 insertions(+), 44 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index 27c6ca0..c725b68 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -44,9 +44,10 @@ static bool wait_for_tpm_stat_cond(struct tpm_chip *chip, u8 mask,
>  	return false;
>  }
>  
> -static int wait_for_tpm_stat(struct tpm_chip *chip, u8 mask,
> -		unsigned long timeout, wait_queue_head_t *queue,
> -		bool check_cancel)
> +static int wait_for_tpm_stat_result(struct tpm_chip *chip, u8 mask,
> +				    u8 mask_result, unsigned long timeout,
> +				    wait_queue_head_t *queue,
> +				    bool check_cancel)

Please do not change the function name.

/Jarkko