Re: [PATCH 2/3] tpm2-cmd: Use dynamic delay to wait for self test result

[Jarkko Sakkinen <jarkko.sakkinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

On Fri, Aug 18, 2017 at 02:15:31PM +0200, Alexander Steffen wrote:
> In order to avoid delaying the code longer than necessary while still
> giving the TPM enough time to execute the self tests asynchronously, start
> with a small delay between two polls and increase it each round.
> 
> Signed-off-by: Alexander Steffen <Alexander.Steffen-d0qZbvYSIPpWk0Htik3J/w@public.gmane.org>
> ---
>  drivers/char/tpm/tpm2-cmd.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> index 7e328d6..e3d4cc3 100644
> --- a/drivers/char/tpm/tpm2-cmd.c
> +++ b/drivers/char/tpm/tpm2-cmd.c
> @@ -877,20 +877,17 @@ static int tpm2_start_selftest(struct tpm_chip *chip, bool full)
>  static int tpm2_do_selftest(struct tpm_chip *chip)
>  {
>  	int rc;
> -	unsigned int loops;
> -	unsigned int delay_msec = 100;
> -	unsigned long duration;
> -	int i;
> -
> -	duration = tpm2_calc_ordinal_duration(chip, TPM2_CC_SELF_TEST);
> +	unsigned int delay_msec = 20;
> +	long duration;
>  
> -	loops = jiffies_to_msecs(duration) / delay_msec;
> +	duration = jiffies_to_msecs(
> +		tpm2_calc_ordinal_duration(chip, TPM2_CC_SELF_TEST));
>  
>  	rc = tpm2_start_selftest(chip, false);
>  	if (rc)
>  		return rc;
>  
> -	for (i = 0; i < loops; i++) {
> +	while (duration > 0) {
>  		/* Attempt to read a PCR value */
>  		rc = tpm2_pcr_read(chip, 0, NULL);
>  		if (rc < 0)
> @@ -900,6 +897,10 @@ static int tpm2_do_selftest(struct tpm_chip *chip)
>  			break;
>  
>  		msleep(delay_msec);
> +		duration -= delay_msec;
> +
> +		/* wait longer the next round */
> +		delay_msec *= 2;
>  	}
>  
>  	return rc;
> -- 
> 2.7.4
> 

Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>

/Jarkko

------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot