From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jerome Brunet Subject: mmc: UHS Voltage switch and operating frequency question Date: Mon, 31 Jul 2017 18:20:04 +0200 Message-ID: <1501518004.2759.5.camel@baylibre.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-wm0-f46.google.com ([74.125.82.46]:38420 "EHLO mail-wm0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751054AbdGaQUH (ORCPT ); Mon, 31 Jul 2017 12:20:07 -0400 Received: by mail-wm0-f46.google.com with SMTP id m85so174776417wma.1 for ; Mon, 31 Jul 2017 09:20:06 -0700 (PDT) Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: Ulf Hansson Cc: Kevin Hilman , "linux-mmc@vger.kernel.org" , "open list:ARM/Amlogic Meson..." Hi Ulf, I am working on adding signal voltage switch callback to the meson mmc driver. While testing, I noticed that a few cards fail to exit the busy state after the voltage switch. After tinkering with the driver a bit, I noticed that increasing the clock frequency from 400kHz to 1MHz solve the problem. Strange, isn't it ? I'm don't know MMC that much but is it possible that some card require a minimum operating frequency to enter UHS mode ? The simplified spec (Part 1 - Physical Layer) says that before CMD11, we should have had CMD41 (Init Command) . After CMD41, the card should be operating at Default Speed or SDR12. I believe that in both case, the frequency is "up to 25Mhz" ? This would be the maximum, but is there a minimum ? 400kHz seems pretty low compared to 25Mhz ... I hope you will able to shed light on this :) Best Regards jerome