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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 61135C47E49 for ; Wed, 30 Oct 2019 12:02:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3166420663 for ; Wed, 30 Oct 2019 12:02:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ti.com header.i=@ti.com header.b="jGjSaZO7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726788AbfJ3MCR (ORCPT ); Wed, 30 Oct 2019 08:02:17 -0400 Received: from lelv0143.ext.ti.com ([198.47.23.248]:46762 "EHLO lelv0143.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726371AbfJ3MCR (ORCPT ); Wed, 30 Oct 2019 08:02:17 -0400 Received: from lelv0265.itg.ti.com ([10.180.67.224]) by lelv0143.ext.ti.com (8.15.2/8.15.2) with ESMTP id x9UC28IS081325; Wed, 30 Oct 2019 07:02:08 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ti.com; s=ti-com-17Q1; t=1572436928; bh=deGeWsxl2NGlv/ZORhmQRP2LBTdRI7RQVc27Zn15SaM=; h=Subject:From:To:CC:References:Date:In-Reply-To; b=jGjSaZO7k4xCh0ML52eeMLJ0DRF9T041rvLLckM4CY5aGSu1iuKFDldYBAVSknvsT Su1dVL345H3TT4MlrhWF9G/Dgu46Cxy1afD2kTWEHeYiIRuM64UNC05zmyIhCq/OOL jVzsI+pUPKF0Lxhr5grQLD3/O+HTrUENpoqI3RrM= Received: from DFLE103.ent.ti.com (dfle103.ent.ti.com [10.64.6.24]) by lelv0265.itg.ti.com (8.15.2/8.15.2) with ESMTPS id x9UC28W5104385 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 30 Oct 2019 07:02:08 -0500 Received: from DFLE115.ent.ti.com (10.64.6.36) by DFLE103.ent.ti.com (10.64.6.24) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1713.5; Wed, 30 Oct 2019 07:02:07 -0500 Received: from fllv0039.itg.ti.com (10.64.41.19) by DFLE115.ent.ti.com (10.64.6.36) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1713.5 via Frontend Transport; Wed, 30 Oct 2019 07:01:54 -0500 Received: from [192.168.2.6] (ileax41-snat.itg.ti.com [10.172.224.153]) by fllv0039.itg.ti.com (8.15.2/8.15.2) with ESMTP id x9UC242e014998; Wed, 30 Oct 2019 07:02:05 -0500 Subject: Re: [RFC 0/2] gpio: Support for shared GPIO lines on boards From: Peter Ujfalusi To: , CC: , , , , , , References: <20191030114530.872-1-peter.ujfalusi@ti.com> Message-ID: <15adbc79-a0df-5c3e-fac4-cf8a3552abfe@ti.com> Date: Wed, 30 Oct 2019 14:03:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191030114530.872-1-peter.ujfalusi@ti.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 30/10/2019 13.45, Peter Ujfalusi wrote: > Hi, > > The shared GPIO line for external components tends to be a common issue and > there is no 'clean' way of handling it. I have missed Rob and the DT list from the recipients list, I'll send the RFC v2 asap. - Péter > I'm aware of the GPIOD_FLAGS_BIT_NONEXCLUSIVE flag, which must be provided when > a driver tries to request a GPIO which is already in use. > However the driver must know that the component is going to be used in such a > way, which can be said to any external components with GPIO line, so in theory > all drivers must set this flag when requesting the GPIO... > > But with the GPIOD_FLAGS_BIT_NONEXCLUSIVE all clients have full control of the > GPIO line. For example any device using the same GPIO as reset/enable line can > reset/enable other devices, which is not something the other device might like > or can handle. > For example a device needs to be configured after it is enabled, but some other > driver would reset it while handling the same GPIO -> the device is not > operational anymmore as it lost it's configuration. > > With the gpio-shared gpiochip we can overcome this by giving the gpio-shared > the role of making sure that the GPIO line only changes state when it will not > disturb any of the clients sharing the same GPIO line. > > The 'sticky' state of the line depends on the board design, which can be > communicated with the hold-active-state property: > > GPIO_ACTIVE_HIGH: the line must be high as long as any of the clients want it to > be high > GPIO_ACTIVE_LOW: the line must be low as long as any of the clients want it to > be low > > In board DTS files it is just adding the node to descibe the shared GPIO line > and point the users of this line to the shared-gpio node instead of the real > GPIO. > > Something like this: > > codec_reset: gpio-shared0 { > compatible = "gpio-shared"; > gpio-controller; > #gpio-cells = <2>; > > root-gpios = <&audio_exp 0 GPIO_ACTIVE_HIGH>; > > branch-count = <2>; > hold-active-state = ; > }; > > &main_i2c3 { > audio_exp: gpio@21 { > compatible = "ti,tca6416"; > reg = <0x21>; > gpio-controller; > #gpio-cells = <2>; > }; > > pcm3168a_a: audio-codec@47 { > compatible = "ti,pcm3168a"; > reg = <0x47>; > > #sound-dai-cells = <1>; > > rst-gpios = <&codec_reset 0 GPIO_ACTIVE_HIGH>; > ... > }; > > pcm3168a_b: audio-codec@46 { > compatible = "ti,pcm3168a"; > reg = <0x46>; > > #sound-dai-cells = <1>; > > rst-gpios = <&codec_reset 1 GPIO_ACTIVE_HIGH>; > ... > }; > }; > > If any of the codec requests the GPIO to be high, the line will go up and will > only going to be low when both of them set's their shared line to low. > > Note: other option would be to have something similar to gpio-hog (gpio-shared) > support in the core itself, but then all of the logic and state handling for the > users of the shared line needs to be moved there. > Simply counting the low and high requests would not work as the GPIO framework > by design does not refcounts the state, iow gpio_set(0) three times and > gpio_set(1) would set the line high. > > I have also looked at the reset framework, but again it can not be applied in a > generic way for GPIOs shared for other purposes and all existing drivers must > be converted to use the reset framework (and adding a linux only warpper on top > of reset GPIOs). > > Regards, > Peter > --- > Peter Ujfalusi (2): > dt-bindings: gpio: Add binding document for shared GPIO > gpio: Add new driver for handling 'shared' gpio lines on boards > > .../devicetree/bindings/gpio/gpio-shared.yaml | 100 ++++++++ > drivers/gpio/Kconfig | 6 + > drivers/gpio/Makefile | 1 + > drivers/gpio/gpio-shared.c | 229 ++++++++++++++++++ > 4 files changed, 336 insertions(+) > create mode 100644 Documentation/devicetree/bindings/gpio/gpio-shared.yaml > create mode 100644 drivers/gpio/gpio-shared.c > Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. 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