From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755558AbdBQFJr (ORCPT ); Fri, 17 Feb 2017 00:09:47 -0500 Received: from mail-pg0-f67.google.com ([74.125.83.67]:35310 "EHLO mail-pg0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750826AbdBQFJo (ORCPT ); Fri, 17 Feb 2017 00:09:44 -0500 Subject: Re: [PATCH 5/5] tpm_tis_spi: Add small delay after last transfer To: Peter Huewe , Jarkko Sakkinen References: <1487261386-2641-5-git-send-email-peter.huewe@infineon.com> Cc: Jason Gunthorpe , tpmdd-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, peterhuewe@gmx.de, Christophe Ricard , stable@vger.kernel.org, Alexander Steffen From: Christophe Ricard Message-ID: Date: Thu, 16 Feb 2017 21:09:42 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <1487261386-2641-5-git-send-email-peter.huewe@infineon.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Are you sure it is not better to introduce this delay directly in the rpi spi driver ? Other than that i don't see any issue with it. On 16/02/2017 08:09, 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 > --- > 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;