linux-kernel - Re: [RESEND][PATCH] tpm: read burstcount from TPM

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Date:	Fri, 1 Jul 2016 11:43:23 +0300
From:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:	apronin@...omium.org
Cc:	Peter Huewe <peterhuewe@....de>,
	Marcel Selhorst <tpmdd@...horst.net>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Christophe Ricard <christophe.ricard@...il.com>,
	tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [RESEND][PATCH] tpm: read burstcount from TPM_STS in one 32-bit
 transaction

On Thu, Jun 30, 2016 at 10:25:43AM -0700, apronin@...omium.org wrote:
> From: Andrey Pronin <apronin@...omium.org>
> 
> Some chips incorrectly support partial reads from TPM_STS register
> at non-zero offsets. Read the entire 32-bits register instead of
> making two 8-bit reads to support such devices and reduce the number
> of bus transactions when obtaining the burstcount from TPM_STS.
> 
> Signed-off-by: Andrey Pronin <apronin@...omium.org>

Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>

/Jarkko

> ---
> 
> No changes. 
> Re-sending to tpmdd-devel member-only list after subscribing.
> 
>  drivers/char/tpm/tpm_tis_core.c | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index 03a06b3..8110b52 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -157,22 +157,17 @@ static int get_burstcount(struct tpm_chip *chip)
>  	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>  	unsigned long stop;
>  	int burstcnt, rc;
> -	u8 value;
> +	u32 value;
>  
>  	/* wait for burstcount */
>  	/* which timeout value, spec has 2 answers (c & d) */
>  	stop = jiffies + chip->timeout_d;
>  	do {
> -		rc = tpm_tis_read8(priv, TPM_STS(priv->locality) + 1, &value);
> +		rc = tpm_tis_read32(priv, TPM_STS(priv->locality), &value);
>  		if (rc < 0)
>  			return rc;
>  
> -		burstcnt = value;
> -		rc = tpm_tis_read8(priv, TPM_STS(priv->locality) + 2, &value);
> -		if (rc < 0)
> -			return rc;
> -
> -		burstcnt += value << 8;
> +		burstcnt = (value >> 8) & 0xFFFF;
>  		if (burstcnt)
>  			return burstcnt;
>  		msleep(TPM_TIMEOUT);
> -- 
> 2.6.6
>