linux-kernel - Re: [PATCH 3/5] tpm_tis_spi: Check correct byte for wait state indicator

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Message-ID: <7aee3c3f-ea63-4dcc-1ed5-04c1b954cc7d@gmail.com>
Date:   Thu, 16 Feb 2017 21:09:30 -0800
From:   Christophe Ricard <christophe.ricard@...il.com>
To:     Peter Huewe <peter.huewe@...ineon.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        peterhuewe@....de, Christophe Ricard <christophe-h.ricard@...com>,
        stable@...r.kernel.org,
        Alexander Steffen <Alexander.Steffen@...ineon.com>
Subject: Re: [PATCH 3/5] tpm_tis_spi: Check correct byte for wait state
 indicator

That's is correct, this is a mistake on my side and never saw it :-(.

I guess it was possibly leading to "waste" at least 1 wait state on some 
TPMs.

Wouldn't it be better to merge that with #1 and update the comment 
consequently?


On 16/02/2017 08:08, Peter Huewe wrote:
> Wait states are signaled in the last byte received from the TPM in
> response to the header, not the first byte. Check rx_buf[3] instead of
> rx_buf[0].
>
> Cc: <stable@...r.kernel.org>
> Fixes: 0edbfea537d1 ("tpm/tpm_tis_spi: Add support for spi phy")
> Signed-off-by: Alexander Steffen <Alexander.Steffen@...ineon.com>
> Signed-off-by: Peter Huewe <peter.huewe@...ineon.com>
> ---
>   drivers/char/tpm/tpm_tis_spi.c | 40 +++++++++++++++++++++-------------------
>   1 file changed, 21 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm_tis_spi.c b/drivers/char/tpm/tpm_tis_spi.c
> index d782b9974c14..16938e2253d2 100644
> --- a/drivers/char/tpm/tpm_tis_spi.c
> +++ b/drivers/char/tpm/tpm_tis_spi.c
> @@ -60,7 +60,7 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u8 len,
>   				u8 *buffer, u8 direction)
>   {
>   	struct tpm_tis_spi_phy *phy = to_tpm_tis_spi_phy(data);
> -	int ret, i;
> +	int ret;
>   	struct spi_message m;
>   	struct spi_transfer spi_xfer = {
>   		.tx_buf = phy->tx_buf,
> @@ -85,25 +85,27 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u8 len,
>   	if (ret < 0)
>   		goto exit;
>   
> -	phy->tx_buf[0] = 0;
> -
> -	/* According to TCG PTP specification, if there is no TPM present at
> -	 * all, then the design has a weak pull-up on MISO. If a TPM is not
> -	 * present, a pull-up on MISO means that the SB controller sees a 1,
> -	 * and will latch in 0xFF on the read.
> -	 */
> -	for (i = 0; (phy->rx_buf[0] & 0x01) == 0 && i < TPM_RETRY; i++) {
> -		spi_xfer.len = 1;
> -		spi_message_init(&m);
> -		spi_message_add_tail(&spi_xfer, &m);
> -		ret = spi_sync_locked(phy->spi_device, &m);
> -		if (ret < 0)
> +	if ((phy->rx_buf[3] & 0x01) == 0) {
> +		// handle SPI wait states
> +		int i;
> +
> +		phy->tx_buf[0] = 0;
> +
> +		for (i = 0; i < TPM_RETRY; i++) {
> +			spi_xfer.len = 1;
> +			spi_message_init(&m);
> +			spi_message_add_tail(&spi_xfer, &m);
> +			ret = spi_sync_locked(phy->spi_device, &m);
> +			if (ret < 0)
> +				goto exit;
> +			if (phy->rx_buf[0] & 0x01)
> +				break;
> +		}
> +
> +		if (i == TPM_RETRY) {
> +			ret = -ETIMEDOUT;
>   			goto exit;
> -	}
> -
> -	if (i == TPM_RETRY) {
> -		ret = -ETIMEDOUT;
> -		goto exit;
> +		}
>   	}
>   
>   	spi_xfer.cs_change = 0;