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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 08F57C43331 for ; Fri, 6 Sep 2019 09:46:17 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D0ACC206A1 for ; Fri, 6 Sep 2019 09:46:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="s38B0HW2" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D0ACC206A1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ACULAB.COM Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:In-Reply-To:References: Message-ID:Date:Subject:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=He9LaoofHJmQ5yy+6AwEP6IEVxMfNUSvFUKqnDX/624=; b=s38B0HW2yc+CSS HMW80T4keEBR79wt/4xENI18bUICwnGSjiHK+hEXMgaVl04ADtWpgWaiXVIs/ixKfwY/Bhvkmuvx1 sNT4UJhZDLoYCe0Bv7gWlZfHp1uTNA8m7SLh76sfCR69BOh8faC98AeE5cvw90dvi2UvLZbJc+ZBO O2rlNKUqIxMbhl2PmzeoEGsZ2YznFlbJGL/qwfzNA7H+81rcQWWwO2VWHPuMoSumspCt9ZyGinnY6 RpqTFkHpU4Auh0fP2oKSmLp3X3uva6urdayumwye+NmaDJb7V4C+w5DPQosyYCyz+oTDbXwdOPB39 FyedhrJTRFEwIfAQQnXQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1i6Aom-0003mg-SJ; Fri, 06 Sep 2019 09:46:12 +0000 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1i6Aoj-0003lw-NM for linux-arm-kernel@lists.infradead.org; Fri, 06 Sep 2019 09:46:11 +0000 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-104-eKY-JNlwMq6UlZLFLzlduw-1; Fri, 06 Sep 2019 10:46:02 +0100 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 6 Sep 2019 10:46:02 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Fri, 6 Sep 2019 10:46:02 +0100 From: David Laight To: 'Alexandre Belloni' Subject: RE: [PATCH v2] pinctrl: at91-pio4: implement .get_multiple and .set_multiple Thread-Topic: [PATCH v2] pinctrl: at91-pio4: implement .get_multiple and .set_multiple Thread-Index: AQHVY/kRQYKuMyjlyU+DkxaSF5MIvaceWwkA///ylwCAABEjEA== Date: Fri, 6 Sep 2019 09:46:02 +0000 Message-ID: References: <20190905144849.24882-1-alexandre.belloni@bootlin.com> <2261eadf98584d13a490f2abd8777d4a@AcuMS.aculab.com> <20190906091212.GF21254@piout.net> In-Reply-To: <20190906091212.GF21254@piout.net> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-MC-Unique: eKY-JNlwMq6UlZLFLzlduw-1 X-Mimecast-Spam-Score: 0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190906_024610_027961_9A79B59E X-CRM114-Status: GOOD ( 16.33 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Linus Walleij , "linux-kernel@vger.kernel.org" , "linux-gpio@vger.kernel.org" , Ludovic Desroches , "Claudiu.Beznea@microchip.com" , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: Alexandre Belloni > Sent: 06 September 2019 10:12 > On 06/09/2019 09:05:36+0000, David Laight wrote: > > From: Alexandre Belloni > > > Implement .get_multiple and .set_multiple to allow reading or setting > > > multiple pins simultaneously. Pins in the same bank will all be switched at > > > the same time, improving synchronization and performances. > > > > Actually it won't 'improve synchronisation', instead it will lead to > > random synchronisation errors and potential metastability if one > > pin is used as a clock and another as data, or if the code is reading > > a free-flowing counter. > > > > It does improve gpio switching synchronisation when they are in the same > bank as it will remove the 250ns delay. Of course, if you need this > delay between clk and data, then the consumer driver should ensure the > delay is present. With multiple requests the output pin changes will always be in the same order and will be separated by (say) 250ns. This is a guaranteed synchronisation. If you change multiple pins with the same 'iowrite()' then the pins will change at approximately the same time. But the actual order will depend on internal device delays (which may depend on the actual silicon and temperature). You then have to take account of varying track lengths and the target devices input stage properties before knowing which change arrives first. The delays might be sub-nanosecond, but they matter if you are talking about synchronisation. IIRC both SMBus and I2C now quote 0ns setup time. Changing both clock and data with the same IOW isn't enough to guarantee this. (In practise the I2C setup time required by a device is probably slightly negative (In order to support 0ns inputs) so a very small -ve setup will (mostly) work.) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel