From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751531AbdBXNEa (ORCPT ); Fri, 24 Feb 2017 08:04:30 -0500 Received: from mga07.intel.com ([134.134.136.100]:18348 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751115AbdBXNEV (ORCPT ); Fri, 24 Feb 2017 08:04:21 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.35,201,1484035200"; d="scan'208";a="1115105998" Date: Fri, 24 Feb 2017 15:00:42 +0200 From: Jarkko Sakkinen To: Peter Huewe Cc: Jason Gunthorpe , tpmdd-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, peterhuewe@gmx.de, Christophe Ricard , stable@vger.kernel.org, Alexander Steffen Subject: Re: [PATCH 5/5] tpm_tis_spi: Add small delay after last transfer Message-ID: <20170224130042.jzxlrhcu72qbf4fs@intel.com> References: <1487261386-2641-5-git-send-email-peter.huewe@infineon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1487261386-2641-5-git-send-email-peter.huewe@infineon.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo User-Agent: Mutt/1.6.2-neo (2016-08-21) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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: > Fixes: 0edbfea537d1 ("tpm/tpm_tis_spi: Add support for spi phy") > Signed-off-by: Alexander Steffen > Signed-off-by: Peter Huewe Reviewed-by: Jarkko Sakkinen /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 >