From patchwork Fri Nov 27 20:04:29 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sebastian Reichel X-Patchwork-Id: 334360 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=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, UNPARSEABLE_RELAY, URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham 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 09E9FC63777 for ; Fri, 27 Nov 2020 23:30:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B7F7322242 for ; Fri, 27 Nov 2020 23:30:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729330AbgK0X26 (ORCPT ); Fri, 27 Nov 2020 18:28:58 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57584 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731430AbgK0UFN (ORCPT ); Fri, 27 Nov 2020 15:05:13 -0500 Received: from bhuna.collabora.co.uk (bhuna.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e3e3]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6C981C0613D4 for ; Fri, 27 Nov 2020 12:05:12 -0800 (PST) Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: sre) with ESMTPSA id 13F9A1F465A8 Received: by jupiter.universe (Postfix, from userid 1000) id C796D4800D9; Fri, 27 Nov 2020 21:05:07 +0100 (CET) From: Sebastian Reichel To: dri-devel@lists.freedesktop.org, Thierry Reding , Sam Ravnborg Cc: linux-omap@vger.kernel.org, kernel@collabora.com, Sebastian Reichel , Jarkko Nikula , Peter Ujfalusi , Tony Lindgren , Aaro Koskinen , Ivaylo Dimitrov , Merlijn Wajer , Laurent Pinchart , Tomi Valkeinen Subject: [PATCH] drm/panel: sony-acx565akm: Fix race condition in probe Date: Fri, 27 Nov 2020 21:04:29 +0100 Message-Id: <20201127200429.129868-1-sebastian.reichel@collabora.com> X-Mailer: git-send-email 2.29.2 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-omap@vger.kernel.org The probe routine acquires the reset GPIO using GPIOD_OUT_LOW. Directly afterwards it calls acx565akm_detect(), which sets the GPIO value to HIGH. If the bootloader initialized the GPIO to HIGH before the probe routine was called, there is only a very short time period of a few instructions where the reset signal is LOW. Exact time depends on compiler optimizations, kernel configuration and alignment of the stars, but I expect it to be always way less than 10us. There are no public datasheets for the panel, but acx565akm_power_on() has a comment with timings and reset period should be at least 10us. So this potentially brings the panel into a half-reset state. The result is, that panel may not work after boot and can get into a working state by re-enabling it (e.g. by blanking + unblanking), since that does a clean reset cycle. This bug has recently been hit by Ivaylo Dimitrov, but there are some older reports which are probably the same bug. At least Tony Lindgren, Peter Ujfalusi and Jarkko Nikula have experienced it in 2017 describing the blank/unblank procedure as possible workaround. Note, that the bug really goes back in time. It has originally been introduced in the predecessor of the omapfb driver in 3c45d05be382 ("OMAPDSS: acx565akm panel: handle gpios in panel driver") in 2012. That driver eventually got replaced by a newer one, which had the bug from the beginning in 84192742d9c2 ("OMAPDSS: Add Sony ACX565AKM panel driver") and still exists in fbdev world. That driver has later been copied to omapdrm and then was used as a basis for this driver. Last but not least the omapdrm specific driver has been removed in 45f16c82db7e ("drm/omap: displays: Remove unused panel drivers"). Reported-by: Jarkko Nikula Reported-by: Peter Ujfalusi Reported-by: Tony Lindgren Reported-by: Aaro Koskinen Reported-by: Ivaylo Dimitrov Cc: Merlijn Wajer Cc: Laurent Pinchart Cc: Tomi Valkeinen Fixes: 1c8fc3f0c5d2 ("drm/panel: Add driver for the Sony ACX565AKM panel") Signed-off-by: Sebastian Reichel Tested-by: Jarkko Nikula Reviewed-by: Laurent Pinchart --- drivers/gpu/drm/panel/panel-sony-acx565akm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/panel/panel-sony-acx565akm.c b/drivers/gpu/drm/panel/panel-sony-acx565akm.c index e95fdfb16b6c..ba0b3ead150f 100644 --- a/drivers/gpu/drm/panel/panel-sony-acx565akm.c +++ b/drivers/gpu/drm/panel/panel-sony-acx565akm.c @@ -629,7 +629,7 @@ static int acx565akm_probe(struct spi_device *spi) lcd->spi = spi; mutex_init(&lcd->mutex); - lcd->reset_gpio = devm_gpiod_get(&spi->dev, "reset", GPIOD_OUT_LOW); + lcd->reset_gpio = devm_gpiod_get(&spi->dev, "reset", GPIOD_OUT_HIGH); if (IS_ERR(lcd->reset_gpio)) { dev_err(&spi->dev, "failed to get reset GPIO\n"); return PTR_ERR(lcd->reset_gpio);