From patchwork Sat Apr 24 14:39:35 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andy Shevchenko X-Patchwork-Id: 426952 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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 41692C43461 for ; Sat, 24 Apr 2021 14:39:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1C3526141C for ; Sat, 24 Apr 2021 14:39:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230211AbhDXOkI (ORCPT ); Sat, 24 Apr 2021 10:40:08 -0400 Received: from mga05.intel.com ([192.55.52.43]:10999 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231892AbhDXOkF (ORCPT ); Sat, 24 Apr 2021 10:40:05 -0400 IronPort-SDR: iC+Si5H8TPS4Cfzd+vuw/f2frozbJuRuojCYbTWWBA8X/MvAJ27QaJyNsSk9sQ9niBe0kgBpPY 6Xh9s41F1b6g== X-IronPort-AV: E=McAfee;i="6200,9189,9964"; a="281510338" X-IronPort-AV: E=Sophos;i="5.82,248,1613462400"; d="scan'208";a="281510338" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Apr 2021 07:39:26 -0700 IronPort-SDR: 1UFCjT/JIVgQx7pO60sjzp0nWUEdweTuGDkLnc3yyMB9L+5ERsdwehb7oFk0LuTBjUUcywowPz 9yPKwz+Kmv+Q== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.82,248,1613462400"; d="scan'208";a="428763423" Received: from black.fi.intel.com ([10.237.72.28]) by orsmga008.jf.intel.com with ESMTP; 24 Apr 2021 07:39:24 -0700 Received: by black.fi.intel.com (Postfix, from userid 1003) id 0E66611E; Sat, 24 Apr 2021 17:39:41 +0300 (EEST) From: Andy Shevchenko To: Andy Shevchenko , "Rafael J. Wysocki" , linux-gpio@vger.kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Mika Westerberg , "Rafael J. Wysocki" , Len Brown Subject: [PATCH v1 1/1] Documentation: firmware-guide: gpio-properties: Add note to SPI CS case Date: Sat, 24 Apr 2021 17:39:35 +0300 Message-Id: <20210424143935.69487-1-andriy.shevchenko@linux.intel.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org Historically ACPI has no means of the GPIO polarity and thus the SPISerialBus() resource defines it on the per-chip basis. In order to avoid an ambiguity, the GPIO polarity is considered being always Active High. Add note about this to the respective documentation file. Signed-off-by: Andy Shevchenko --- Documentation/firmware-guide/acpi/gpio-properties.rst | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/Documentation/firmware-guide/acpi/gpio-properties.rst b/Documentation/firmware-guide/acpi/gpio-properties.rst index 4e264c16ddff..df4b711053ee 100644 --- a/Documentation/firmware-guide/acpi/gpio-properties.rst +++ b/Documentation/firmware-guide/acpi/gpio-properties.rst @@ -99,6 +99,12 @@ native:: } } +Note, that historically ACPI has no means of the GPIO polarity and thus +the SPISerialBus() resource defines it on the per-chip basis. In order +to avoid a chain of negations, the GPIO polarity is considered being +Active High. Even for the cases when _DSD() is involved (see the example +above) the GPIO CS polarity must be defined Active High to avoid ambiguity. + Other supported properties ==========================