From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Nelson Subject: Re: Devicetree: Initialization order of mmc block devices? Date: Wed, 18 Jul 2012 07:54:43 -0700 Message-ID: <5006CE33.2040205@boundarydevices.com> References: <5006571A.7060103@de.bosch.com> <50068696.8070408@de.bosch.com> <5006C40D.300@de.bosch.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-gg0-f174.google.com ([209.85.161.174]:59539 "EHLO mail-gg0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750863Ab2GROyr (ORCPT ); Wed, 18 Jul 2012 10:54:47 -0400 Received: by gglu4 with SMTP id u4so1637243ggl.19 for ; Wed, 18 Jul 2012 07:54:46 -0700 (PDT) In-Reply-To: <5006C40D.300@de.bosch.com> Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: Knut Wohlrab Cc: Jassi Brar , "Behme Dirk (CM-AI/PJ-CF32)" , "linux-mmc@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" On 07/18/2012 07:11 AM, Knut Wohlrab wrote: > On 07/18/2012 03:47 PM, Jassi Brar wrote: >> On 18 July 2012 15:19, Knut Wohlrab wrote: >> >>> If a SD card is inserted at boot time, its "mmcblk0", the embedded >>> MMC (eMMC) device "mmcblk1". This makes it difficult to give the kernel the >>> correct device for the eMMC root file system ("root=/dev/mmcblk?p1 ..."). >>> >> How about root=UUID= ? > Because we are talking about an embedded device, it is very difficult to get a > UUID of a eMMC partition into kernel command line with U-Boot. Handling of UUID > is also a big effort at board manufacturing. > > Startup speed is very important for us. Searching for UUID on several MMC/SD > devices will significant slow down the boot process. > > This problem can occur on many devices with embedded MMC and removable SD, e.g. > smart phones. So I think we should find an solution to define MMC scan order or > device number/name in a device tree. > Isn't /dev/disk/by-path what you're after? ~$ ls -l /dev/disk/by-path/ lrwxrwxrwx 1 root root 13 Jan 1 15:22 platform-mmc0:b368 -> ../../mmcblk0 lrwxrwxrwx 1 root root 15 Jan 1 15:22 platform-mmc0:b368-part1 -> ../../mmcblk0p1 lrwxrwxrwx 1 root root 15 Jan 1 15:22 platform-mmc0:b368-part2 -> ../../mmcblk0p2 lrwxrwxrwx 1 root root 15 Jan 1 15:22 platform-mmc0:b368-part3 -> ../../mmcblk0p3