From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751367AbaKYF3d (ORCPT ); Tue, 25 Nov 2014 00:29:33 -0500 Received: from mail-vc0-f170.google.com ([209.85.220.170]:45124 "EHLO mail-vc0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750945AbaKYF3a (ORCPT ); Tue, 25 Nov 2014 00:29:30 -0500 MIME-Version: 1.0 In-Reply-To: References: <1415109789-7046-1-git-send-email-addy.ke@rock-chips.com> <1415678573-6093-1-git-send-email-addy.ke@rock-chips.com> <5464152E.7040209@rock-chips.com> Date: Mon, 24 Nov 2014 21:29:28 -0800 X-Google-Sender-Auth: f7dAc0dkfwTNFtnEKWxmHmF1rxg Message-ID: Subject: Re: [PATCH] mmc: dw_mmc: try pick the exact same voltage as vmmc for vqmmc From: Doug Anderson To: Ulf Hansson Cc: addy ke , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Randy Dunlap , "tgih.jun@samsung.com" , Jaehoon Chung , Chris Ball , Dinh Nguyen , =?UTF-8?Q?Heiko_St=C3=BCbner?= , Olof Johansson , Sonny Rao , Alexandru Stan , "devicetree@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , linux-mmc , "linux-arm-kernel@lists.infradead.org" , "open list:ARM/Rockchip SoC..." , "zhenfu.fang" , Eddie Cai , lintao , chenfen , zyf , Jianqun Xu , Tao Huang , Chris Zhong , =?UTF-8?B?5aea5pm65oOF?= , han jiang , Kever Yang , zhangqing , Lin Huang Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ulf, On Mon, Nov 24, 2014 at 5:29 AM, Ulf Hansson wrote: >> 2. Several people I've talked to have expressed concerns that our >> minimum value is 2.7V. Apparently that's really on the edge and makes >> EEs a little nervous. The quick sample of cards sitting on my desk >> shows that they seem to claim 0x00ff8000, which doesn't include 2.7V. > > 0x00ff8000 states what values of VDD levels the device supports. Not VIO. Yup, I was just pointing out that possibly others were trying to get a little bit of margin (not going all the way down to 2.7V) too. >> Both of the above make me feel like dw_mmc should try its best to pick >> a value for vqmmc that is closest to the value of vmmc (and >= 2.7V). >> That also happens to make us work exactly like hosts where vmmc and >> vqmmc are supplied by the same supply. > > I do see your point. And I agree that it would be nice to achieve > something like this. > > The question is how to do this. For sure, we need to involve the mmc > core to handle this correctly. You could add a function to the core that we could call from dw_mci_switch_voltage() and it would do all the work except trying to set the UHS register. That would certainly make it easy. That could try to set the highest voltage that is <= vmmc when we're at MMC_SIGNAL_VOLTAGE_330. -Doug