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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id C4BCBC433F5 for ; Wed, 24 Nov 2021 05:44:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:Subject: From:References:Cc:To:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=u4slCKFgxhMisneHFaIp6p/04YW6ePsMSkQIlavuYfw=; b=lJKpYN8cJUzRniJe3jVEy1/uvs MQEPF97hbYb9Nujwvb7ewSZRw2o7wkZCTr0R8sEj0W2zNR7oSepOCOafaHB3lvrNqbTHOyNXfVquA WUYF9mR9gz70rVXc+GYLt4SpUvdavPoLZjhYriF1fkMHAav4dJeA9ZTWK+ItzdTK5lDtWvZjO0+B3 2kF6Ko2GmI4smJdHPt/b7cQlhhfJTn2O4PHL1gWr3E/Y7Y0x24VaDEQjnA9D14H5tPrV0CxeTAuP/ gWVI7oYPN7Fq2IZIqaRrWk0pelqA3wctSQCEXW56znWn5d5vWiWy8la0+WLlzuT6q5blV0+QWocuh 0NRd+MNw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mpl38-003xIT-1F; Wed, 24 Nov 2021 05:42:30 +0000 Received: from marcansoft.com ([212.63.210.85] helo=mail.marcansoft.com) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mpl33-003xHs-CD for linux-arm-kernel@lists.infradead.org; Wed, 24 Nov 2021 05:42:27 +0000 Received: from [127.0.0.1] (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: marcan@marcan.st) by mail.marcansoft.com (Postfix) with ESMTPSA id 5D4774268D; Wed, 24 Nov 2021 05:42:15 +0000 (UTC) To: Linus Walleij Cc: Janne Grunau , Sven Peter , Alyssa Rosenzweig , Rob Herring , linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20211122225807.8105-1-j@jannau.net> <20211122225807.8105-4-j@jannau.net> <5f16c962-72a1-21ec-9651-744053f74365@marcan.st> From: Hector Martin Subject: Re: [PATCH v3 3/4] arm64: dts: apple: t8103: Add i2c nodes Message-ID: Date: Wed, 24 Nov 2021 14:42:12 +0900 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Language: es-ES X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211123_214225_610836_74EC2F02 X-CRM114-Status: GOOD ( 14.80 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 24/11/2021 08.26, Linus Walleij wrote: > On Tue, Nov 23, 2021 at 3:43 PM Hector Martin wrote: > >> For those following along in the list: the reason why i2c3 was getting >> stuck is because it seems the unused bus is weakly pulled low on these >> machines, which jams it. > > That looks like some power saving attempt. > > I suppose that means that even i2c buses that are in use > could be weakly pulled low when suspending the system > and maybe even inbetween transactions to save some > leak current. Pulled up vs. down dosn't really result in better power savings; neither state will necessarily have more leakage. I think it's just that the pins are completely disconnected, and there's some very minor leakage to ground (megaohms will do) that ends up pulling them down. Pulling down an I2C bus between transactions is not legal; the idle state has to be high. Apple are actually not very good at configuring GPIOs for power saving; e.g. the I/Os for that unused i2c bus still have their input buffers turned on, which is a waste of power. If they wanted to save the smallest drop of power they'd turn that off. But the effect of this is so trivial it probably makes no difference in the context of a laptop, nevermind a desktop like the Mac Mini. -- Hector Martin (marcan@marcan.st) Public Key: https://mrcn.st/pub _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel