From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by yocto-www.yoctoproject.org (Postfix, from userid 118) id 0E5ABE00830; Mon, 20 Apr 2015 05:53:23 -0700 (PDT) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on yocto-www.yoctoproject.org X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham version=3.3.1 X-Spam-HAM-Report: * -1.9 BAYES_00 BODY: Bayes spam probability is 0 to 1% * [score: 0.0000] Received: from sip2-98.nexcess.net (iwavesystems.com [207.32.180.10]) by yocto-www.yoctoproject.org (Postfix) with ESMTP id AE835E00830 for ; Mon, 20 Apr 2015 05:53:18 -0700 (PDT) Received: (qmail 14413 invoked by uid 108); 20 Apr 2015 08:53:17 -0400 Received: from unknown (HELO ?192.168.2.104?) (124.124.219.230) by sip2-98.nexcess.net with SMTP; 20 Apr 2015 08:53:17 -0400 Message-ID: <5534F6BA.3020802@iwavesystems.com> Date: Mon, 20 Apr 2015 18:23:14 +0530 From: ansaris User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Lauren Post , Andrea Scian References: <55310495.1050005@iwavesystems.com> <5531699B.5030204@dave-tech.it> In-Reply-To: Cc: "meta-freescale@yoctoproject.org" Subject: Re: iMX6 - CPU frequency lowered during LDO bypass setting X-BeenThere: meta-freescale@yoctoproject.org X-Mailman-Version: 2.1.13 Precedence: list List-Id: Usage and development list for the meta-fsl-* layers List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 20 Apr 2015 12:53:23 -0000 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Dear Lauren Post, Thank you for your valuable input. Regards, Ansari On Monday 20 April 2015 06:14 PM, Lauren Post wrote: > I forwarded your question to our engineering team and got this answer > > Firstly, we have to decrease VDDARM_IN from 1.375V to 1.175V @792Mhz before LDO bypass mode enabled, otherwise there is window that VDDARM_IN keep 1.375V (violate rule VDDARM_IN <=1.3V in ldo-bypass mode)after LDO bypass mode enabled but before kernel cpufreq change with 1.175V@792Mhz. > Secondly, there is also narrow window that VDDARM_IN in 1.175V with ldo-enabled mode after VDDARM_IN decreased from 1.375V to 1.175V but before ldo-bypass mode enabled. VDDARM_IN 1.175V@792Mhz in ldo-enable mode also violate the rule >= 1.275V. So we have to decrease CPU frequency to 396Mhz to make all voltage setting mach the data sheet. > > Lauren Post > > -----Original Message----- > From: meta-freescale-bounces@yoctoproject.org [mailto:meta-freescale-bounces@yoctoproject.org] On Behalf Of Andrea Scian > Sent: Friday, April 17, 2015 3:14 PM > To: ansaris@iwavesystems.com > Cc: meta-freescale@yoctoproject.org > Subject: Re: [meta-freescale] iMX6 - CPU frequency lowered during LDO bypass setting > > > Il 17/04/2015 15:03, ansaris ha scritto: >> We would like to know, during the LDO bypass settings why the CPU >> frequency is lowered in File-1(Linux 3.14.28_1.0.0-GA)? Is it >> recommended to do the same.? > I think that the answer is here: > > http://git.freescale.com/git/cgit.cgi/imx/uboot-imx.git/commit/?id=404fd02e96d33840f58f83f88815e2a259cdc532 > > During bypass procedure you violate datasheet power constraint if running at 800MHz: in LDO mode VDD_ARM must be 125mV higher that the LDO output voltage, while you need to lower VDD_ARM (on PMIC) before switching to bypass mode. > To fill the 125mV gap you need to: > - switch to 400MHz > - lower PMIC voltages > - switch to bypass mode (which remove the 125mV gap) > - switch back to 800MHz > > If you skip the first step you may have 1.175-0.125 = 1.050V which is below the required power supply for VDD_ARM > > I think this is the meaning of the commit, please correct me if I'm wrong, of course. > > Kind Regards, >