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 shelob.surriel.com (shelob.surriel.com [96.67.55.147]) (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 94BF7EC8727 for ; Thu, 7 Sep 2023 13:57:27 +0000 (UTC) Received: from localhost ([::1] helo=shelob.surriel.com) by shelob.surriel.com with esmtp (Exim 4.96) (envelope-from ) id 1qeFUX-0004Ik-0l; Thu, 07 Sep 2023 09:56:17 -0400 Received: from [2001:4d48:ad52:32c8:5054:ff:fe00:142] (helo=pandora.armlinux.org.uk) by shelob.surriel.com with esmtps (TLS1.2) tls TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1qeFUV-0004IZ-1e for kernelnewbies@kernelnewbies.org; Thu, 07 Sep 2023 09:56:15 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=v3uvxlhpyVywOeCKfN58HL4kywyDPvCRWTa4uTmYA0Q=; b=cMBALboLcZQB/DNbVCwH0r0KjF FKs6pkrAoiU6XIpNGn6ZT3ykUCQ+Ce5ru2X0LJN/wi1zO4BFrFy21XM5xRndzViVJHmSjNc23KM3N 3tHi+R6HNKVPol+fFZa4SUU5JmE19W1F8uRQb4sBvD8S6qVOGhJkdmL6rX/MYhPu1mT0Zt525MV9j eQSsMWb9eZ/3yo6lAKWimBG3nTiy46dA0Vtoz8gVCUe0LTXe+6kaVdpkOeMBO8TclVjgR+WTH2Za/ 2mE5feR0C2jb11Owc26U78mi0p48ztIJuDaE635wnsqQdt0kRDvrdA7s0FDVSpDB14sWBKXvW2n9w vEI7gVwQ==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:57708) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1qeFUF-0003KZ-1Y; Thu, 07 Sep 2023 14:55:59 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1qeFUF-0005tY-7p; Thu, 07 Sep 2023 14:55:59 +0100 Date: Thu, 7 Sep 2023 14:55:59 +0100 From: "Russell King (Oracle)" To: Bagas Sanjaya Subject: Re: Debugging i2c : i2cdetect cant detect a device on i2c line Message-ID: References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Cc: Linux Devicetree , Conor Dooley , Andi Shyti , kernelnewbies@kernelnewbies.org, Linus Walleij , LKML , Rob Herring , Linux I2C , Krzysztof Kozlowski , Raul Piper , Linux ARM X-BeenThere: kernelnewbies@kernelnewbies.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Learn about the Linux kernel List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kernelnewbies-bounces@kernelnewbies.org On Thu, Sep 07, 2023 at 08:36:32PM +0700, Bagas Sanjaya wrote: > [also Cc: devicetree and ARM folks] > > On Thu, Sep 07, 2023 at 08:21:44AM +0530, Raul Piper wrote: > > Hello , > > I am trying to detect an i2c device A on i2c1 line on one of the Arm > > Cortex A7 platform but not able to see any device on a given address ( > > 0x3d) . > > > > Is there any parameters of i2c which i can change like rise/fall time > > , timeout etc in a device tree or kernel source and re test it? > > I have tried changing the i2c speed from 100KHz to 400 KHz but no success. > > I have even tried removing the 1.5K pull ups on the i2c lines but no result. Honestly, from this description, I'm wondering if this posting is a joke. I2C is entirely _reliant_ on pull-ups. It's a wire-or bus, and the logic 1 state is created by no device pulling the signal low, thereby allowing the pull-up resistor to pull the line to the logic 1 state. The pull-up must be the correct strength for the devices on the bus. If it is too strong, then a driver may not be able to pull the signal sufficiently low for other devices to register it as a logic 0. Conversely, the pull-up must be strong enough so that the rise-time of the signal is sufficient to register as a logic 1. If it's a problem with the rise time, then increasing the clock rate will just make the situation worse. So, if other devices work on the bus, it could be that the Vil threshold of this device is not being achieved, whereas the other devices are happy. Therefore, I would suggest you study the data sheets of the device that isn't being detected. Lastly, if the undetectable device has a reset line, it's possible that the device isn't responding because it's being held in reset. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last! _______________________________________________ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies