From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753362AbaKLSEg (ORCPT ); Wed, 12 Nov 2014 13:04:36 -0500 Received: from mail-vc0-f172.google.com ([209.85.220.172]:44729 "EHLO mail-vc0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753100AbaKLSEc (ORCPT ); Wed, 12 Nov 2014 13:04:32 -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> Date: Wed, 12 Nov 2014 10:04:31 -0800 X-Google-Sender-Auth: v5XigoLlAd-ZniS69gQYB8DOM8g 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 Tue, Nov 11, 2014 at 12:52 AM, Ulf Hansson wrote: > On 11 November 2014 05:02, Addy Ke wrote: >> SD2.0 cards need vqmmc and vmmc to be the same. > > No, that's not correct. > > If I remember the spec correctly, the bus signal threshold is 0.75 * VDD. As usual, I will first state my utter lack of knowledge of all things mmc. Now that's out of the way, on two separate board with two separate SoCs I've heard stories of cards that don't work when there's a big gap between vmmc and vqmmc. If my memory serves, previously I heard of problems with vmmc=3.3V and vqmmc=2.8V. That means there were problems with .85 * VDD. Certainly Addy seems to have a card that has problems with vmmc=3.3V and vqmmc=2.7V (but worked with vmmc=3.3V and vqmmc=2.8V). That is .82 * VDD. I have no idea if these old cards are "to spec", but they exist and it would be nice to support them. It seems like the absolute safest thing would be to try to keep vmmc and vqmmc matching if possible, especially during card probe. Once voltage negotiation happened then the vqmmc could go down. >> But vqmmc call regulator_set_voltage to set min_uv(2.7v) as far as possible. > > I guess you want to do that to save as much power as possible. I don't think it's Addy wanting it, I think it's the regulator framework. If a regulator is current 1.8V and you request 2.7 - 3.3V, the framework needs to pick one of those voltages. I believe it will pick 2.7V. ...so I think we get into trouble only when the 2.0 card is plugged in after a UHS card has negotiated down the voltage, but I could be wrong. Maybe Addy can clarify. >> @@ -1163,8 +1163,14 @@ static int dw_mci_switch_voltage(struct mmc_host *mmc, struct mmc_ios *ios) >> */ >> uhs = mci_readl(host, UHS_REG); >> if (ios->signal_voltage == MMC_SIGNAL_VOLTAGE_330) { >> - min_uv = 2700000; >> - max_uv = 3600000; >> + /* try pick the exact same voltage as vmmc for vqmmc */ > > This seems like a generic SD protocol issue. > > Should we maybe provide some helper function from the mmc core, which > in principle take the negotiated card->ocr into account while > calculating the signal voltage level. Typically min_uv should be 0.75 > x (card->ocr), for these cases. Yes, if there are ways to make the solution more generic I would certainly support that. -Doug