From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753283AbdK1QZx (ORCPT ); Tue, 28 Nov 2017 11:25:53 -0500 Received: from hqemgate15.nvidia.com ([216.228.121.64]:15232 "EHLO hqemgate15.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751979AbdK1QZv (ORCPT ); Tue, 28 Nov 2017 11:25:51 -0500 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Tue, 28 Nov 2017 08:25:50 -0800 Subject: Re: [PATCH V2 1/2] mfd: cros ec: spi: Don't send first message too soon To: Lee Jones CC: , , "Brian Norris" , Shawn Nematbakhsh , Benson Leung , References: <1510670608-19594-1-git-send-email-jonathanh@nvidia.com> From: Jon Hunter Message-ID: <419f195f-8c38-5dd2-7742-3fff98d6795b@nvidia.com> Date: Tue, 28 Nov 2017 16:25:44 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <1510670608-19594-1-git-send-email-jonathanh@nvidia.com> X-Originating-IP: [10.21.132.149] X-ClientProxiedBy: UKMAIL102.nvidia.com (10.26.138.15) To UKMAIL101.nvidia.com (10.26.138.13) Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Lee, On 14/11/17 14:43, Jon Hunter wrote: > On the Tegra124 Nyan-Big chromebook the very first SPI message sent to > the EC is failing. > > The Tegra SPI driver configures the SPI chip-selects to be active-high > by default (and always has for many years). The EC SPI requires an > active-low chip-select and so the Tegra chip-select is reconfigured to > be active-low when the EC SPI driver calls spi_setup(). The problem is > that if the first SPI message to the EC is sent too soon after > reconfiguring the SPI chip-select, it fails. > > The EC SPI driver prevents back-to-back SPI messages being sent too > soon by keeping track of the time the last transfer was sent via the > variable 'last_transfer_ns'. To prevent the very first transfer being > sent too soon, initialise the 'last_transfer_ns' variable after calling > spi_setup() and before sending the first SPI message. > > Cc: > > Signed-off-by: Jon Hunter > Reviewed-by: Brian Norris > --- > Changes since V1: > - Added stable-tag and Brian's reviewed-by. > > Looks like this issue has been around for several Linux releases now > and it just depends on timing if this issue is seen or not and so there > is no specific commit this fixes. However, would be good to include for > v4.15. > > drivers/mfd/cros_ec_spi.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c > index c9714072e224..a14196e95e9b 100644 > --- a/drivers/mfd/cros_ec_spi.c > +++ b/drivers/mfd/cros_ec_spi.c > @@ -667,6 +667,7 @@ static int cros_ec_spi_probe(struct spi_device *spi) > sizeof(struct ec_response_get_protocol_info); > ec_dev->dout_size = sizeof(struct ec_host_request); > > + ec_spi->last_transfer_ns = ktime_get_ns(); > > err = cros_ec_register(ec_dev); > if (err) { Can you queue this as a fix for v4.15-rc1? Cheers Jon -- nvpublic