From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ulf Hansson Subject: Re: [PATCH] mmc: dw_mmc: Add support for multiple SD cards on one host interface Date: Mon, 2 Oct 2017 09:12:30 +0200 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: Received: from mail-it0-f53.google.com ([209.85.214.53]:56762 "EHLO mail-it0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751133AbdJBHMb (ORCPT ); Mon, 2 Oct 2017 03:12:31 -0400 Received: by mail-it0-f53.google.com with SMTP id g18so6236746itg.5 for ; Mon, 02 Oct 2017 00:12:31 -0700 (PDT) In-Reply-To: Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: Bernd Edlinger Cc: "linux-mmc@vger.kernel.org" , Jaehoon Chung On 30 September 2017 at 17:39, Bernd Edlinger wrote: > > Needs external logic to multiplex the clock signal, > which is controlled by a GPIO output pin. > > Only the selected SD card receives the clock, > while the other SD card's clock is forced to LOW. > DATA and CMD lines can be connected to both SD cards. > > On warm-start UBOOT should use a sequence of > CMD12 and CMD7 with RCA=0 to force any active SD card > to stop transmission and release the DATA bus. I doubt that is sufficient to support multiple slots. Sometimes the mmc core needs to perform a sequence of operations towards *one* host/card and that must be done in guaranteed manner, to that no other operations are performed for another card/host in-between. Perhaps if you are lucky you may get something that is very fragile to work, but in the end I think the core needs to play along. Moreover, dw_mmc has recently removed its multiple slot support - simply because the complexity wasn't worth it. Unless Jaehoon have changed his mind, I am not going to pick this up. [...] Kind regards Uffe