From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 17250C433E0 for ; Mon, 15 Jun 2020 10:03:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F29022068E for ; Mon, 15 Jun 2020 10:03:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729384AbgFOKDp (ORCPT ); Mon, 15 Jun 2020 06:03:45 -0400 Received: from mga03.intel.com ([134.134.136.65]:16860 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728870AbgFOKDp (ORCPT ); Mon, 15 Jun 2020 06:03:45 -0400 IronPort-SDR: pLpENJn9QAVHEgbzlkf8tCj2nOiC8BcKatYIgXNKryG0avQqo0jPJ6npgibdlfSSAldwqiI1w4 FLM2YmopY9yw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jun 2020 03:03:44 -0700 IronPort-SDR: +py//jfznaYXc5CS6urs2q6OTzdbAlRvDgU5gRTIN1LqW5FfWCojOgbcRHg33Vfzn1VwtY3Y3r VebPBXBuO33Q== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,514,1583222400"; d="scan'208";a="298466856" Received: from smile.fi.intel.com (HELO smile) ([10.237.68.40]) by fmsmga004.fm.intel.com with ESMTP; 15 Jun 2020 03:03:42 -0700 Received: from andy by smile with local (Exim 4.94) (envelope-from ) id 1jklxx-00DXdQ-9y; Mon, 15 Jun 2020 13:03:45 +0300 Date: Mon, 15 Jun 2020 13:03:45 +0300 From: Andy Shevchenko To: Mika Westerberg Cc: Hans de Goede , Linus Walleij , linux-gpio@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] pinctrl: baytrail: Fix pin being driven low for a while on gpiod_get(..., GPIOD_OUT_HIGH) Message-ID: <20200615100345.GV2428291@smile.fi.intel.com> References: <20200606093150.32882-1-hdegoede@redhat.com> <20200608105953.GC247495@lahna.fi.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200608105953.GC247495@lahna.fi.intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Sender: linux-gpio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org On Mon, Jun 08, 2020 at 01:59:53PM +0300, Mika Westerberg wrote: > On Sat, Jun 06, 2020 at 11:31:50AM +0200, Hans de Goede wrote: > > The pins on the Bay Trail SoC have separate input-buffer and output-buffer > > enable bits and a read of the level bit of the value register will always > > return the value from the input-buffer. > > > > The BIOS of a device may configure a pin in output-only mode, only enabling > > the output buffer, and write 1 to the level bit to drive the pin high. > > This 1 written to the level bit will be stored inside the data-latch of the > > output buffer. > > > > But a subsequent read of the value register will return 0 for the level bit > > because the input-buffer is disabled. This causes a read-modify-write as > > done by byt_gpio_set_direction() to write 0 to the level bit, driving the > > pin low! > > > > Before this commit byt_gpio_direction_output() relied on > > pinctrl_gpio_direction_output() to set the direction, followed by a call > > to byt_gpio_set() to apply the selected value. This causes the pin to > > go low between the pinctrl_gpio_direction_output() and byt_gpio_set() > > calls. > > > > Change byt_gpio_direction_output() to directly make the register > > modifications itself instead. Replacing the 2 subsequent writes to the > > value register with a single write. > > > > Note that the pinctrl code does not keep track internally of the direction, > > so not going through pinctrl_gpio_direction_output() is not an issue. > > > > This issue was noticed on a Trekstor SurfTab Twin 10.1. When the panel is > > already on at boot (no external monitor connected), then the i915 driver > > does a gpiod_get(..., GPIOD_OUT_HIGH) for the panel-enable GPIO. The > > temporarily going low of that GPIO was causing the panel to reset itself > > after which it would not show an image until it was turned off and back on > > again (until a full modeset was done on it). This commit fixes this. > > > > This commit also updates the byt_gpio_direction_input() to use direct > > register accesses instead of going through pinctrl_gpio_direction_input(), > > to keep it consistent with byt_gpio_direction_output(). > > > > Note for backporting, this commit depends on: > > commit e2b74419e5cc ("pinctrl: baytrail: Replace WARN with dev_info_once > > when setting direct-irq pin to output") > > > > Cc: stable@vger.kernel.org > > Fixes: 86e3ef812fe3 ("pinctrl: baytrail: Update gpio chip operations") > > Signed-off-by: Hans de Goede > > Acked-by: Mika Westerberg Pushed to my review and testing queue, thanks! -- With Best Regards, Andy Shevchenko