Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753974AbdDKKoo (ORCPT ); Tue, 11 Apr 2017 06:44:44 -0400 Received: from mail-vk0-f42.google.com ([209.85.213.42]:32917 "EHLO mail-vk0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753159AbdDKKnl (ORCPT ); Tue, 11 Apr 2017 06:43:41 -0400 MIME-Version: 1.0 In-Reply-To: References: <1491895862-7952-1-git-send-email-richard.leitner@skidata.com> From: Ulf Hansson Date: Tue, 11 Apr 2017 12:43:39 +0200 Message-ID: Subject: Re: [PATCH v2] mmc: core: add mmc-card hardware reset enable support To: Linus Walleij Cc: Richard Leitner , Bart Van Assche , Luca Porzio , Rob Herring , Mark Rutland , Shawn Lin , Adrian Hunter , Jaehoon Chung , "linux-mmc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "devicetree@vger.kernel.org" , Richard Leitner Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1604 Lines: 45 On 11 April 2017 at 10:17, Linus Walleij wrote: > On Tue, Apr 11, 2017 at 9:31 AM, Richard Leitner > wrote: > >> Some eMMCs disable their hardware reset line (RST_N) by default. To enable >> it the host must set the corresponding bit in ECSD. An example for such >> a device is the Micron MTFCxGACAANA-4M. >> >> This patch adds a new mmc-card devicetree property to let the host enable >> this feature during card initialization. >> >> Signed-off-by: Richard Leitner > > Do we know *WHY* these cards disable their hardware reset lines? Allow me to make a guess. In case the reset isn't enabled, the internal eMMC card firmware don't monitor the pin for the reset. I guess that could makes sense if SoC vendors has failed to properly connect the pin, avoiding the eMMC card to be reset when it shouldn't. > > If it is just some random over-cautious panic thing we might consider > just force re-enableing it, maybe with a warning in the dmesg, so we can > always reset the card. No DT property needed. There is actually already a DT property "cap-mmc-hw-reset" (MMC_CAP_HW_RESET), which tells whether the eMMC reset is supported by the host. Perhaps we can consider to force-enabling it for the eMMC card, when this property is set for the mmc host!? At least, inventing yet another binding doesn't make sense to me. > > Putting some people who work for eMMC vendors in the To: line so they > can say if they know about this. Yes, let's see what they say about it. > > Yours, > Linus Walleij Kind regards Uffe