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Message-ID: <20160701084323.GA15718@intel.com>
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
>
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