linux-kernel - Re: [PATCH 5/5] tpm_tis_spi: Add small delay after last transfer

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Date:   Fri, 24 Feb 2017 15:00:42 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Peter Huewe <peter.huewe@...ineon.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 5/5] tpm_tis_spi: Add small delay after last transfer

On Thu, Feb 16, 2017 at 04:09:46PM +0000, Peter Huewe wrote:
> Testing the implementation with a Raspberry Pi 2 showed that under some
> circumstances its SPI master erroneously releases the CS line before the
> transfer is complete, i.e. before the end of the last clock. In this case
> the TPM ignores the transfer and misses for example the GO command. The
> driver is unable to detect this communication problem and will wait for a
> command response that is never going to arrive, timing out eventually.
> 
> As a workaround, the small delay ensures that the CS line is held long
> enough, even with a faulty SPI master. Other SPI masters are not affected,
> except for a negligible performance penalty.
> 
> 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>

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

/Jarkko

> ---
>  drivers/char/tpm/tpm_tis_spi.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/char/tpm/tpm_tis_spi.c b/drivers/char/tpm/tpm_tis_spi.c
> index b50c5b072df3..685c51bf5d7e 100644
> --- a/drivers/char/tpm/tpm_tis_spi.c
> +++ b/drivers/char/tpm/tpm_tis_spi.c
> @@ -110,6 +110,7 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u8 len,
>  
>  		spi_xfer.cs_change = 0;
>  		spi_xfer.len = transfer_len;
> +		spi_xfer.delay_usecs = 5;
>  
>  		if (direction) {
>  			spi_xfer.tx_buf = NULL;
> -- 
> 2.7.4
>