From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755318AbdKNOoo (ORCPT ); Tue, 14 Nov 2017 09:44:44 -0500 Received: from hqemgate16.nvidia.com ([216.228.121.65]:19954 "EHLO hqemgate16.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754590AbdKNOog (ORCPT ); Tue, 14 Nov 2017 09:44:36 -0500 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Tue, 14 Nov 2017 06:44:36 -0800 Subject: Re: [PATCH 1/2] mfd: cros ec: spi: Don't send first message too soon To: Brian Norris CC: Lee Jones , , , Shawn Nematbakhsh , Benson Leung , Doug Anderson References: <1510607140-30582-1-git-send-email-jonathanh@nvidia.com> <20171113211900.GA126873@google.com> From: Jon Hunter Message-ID: <1ef0189a-13b1-b35d-27b9-61b5f77a1795@nvidia.com> Date: Tue, 14 Nov 2017 14:44:31 +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: <20171113211900.GA126873@google.com> X-Originating-IP: [10.21.132.144] X-ClientProxiedBy: UKMAIL101.nvidia.com (10.26.138.13) 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 On 13/11/17 21:19, Brian Norris wrote: > + others > > On Mon, Nov 13, 2017 at 09:05:39PM +0000, 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. >> >> Signed-off-by: Jon Hunter >> --- >> 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. > > I wonder if that doesn't mean we should have a stable tag still? > > Cc: I was thinking about that as well after I sent it. I have resent as a V2 CC'ing stable. Cheers Jon -- nvpublic