From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753695Ab2KTXs0 (ORCPT ); Tue, 20 Nov 2012 18:48:26 -0500 Received: from mail-ob0-f174.google.com ([209.85.214.174]:57069 "EHLO mail-ob0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753082Ab2KTXsZ (ORCPT ); Tue, 20 Nov 2012 18:48:25 -0500 MIME-Version: 1.0 In-Reply-To: References: Date: Tue, 20 Nov 2012 15:48:24 -0800 X-Google-Sender-Auth: pGfZAr_iBxUk9iQjiYJW0TeWwPY Message-ID: Subject: Re: Device tree node to major/minor? From: Simon Glass To: Grant Likely Cc: lk , Devicetree Discuss , Che-liang Chiou Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Grant, On Tue, Nov 20, 2012 at 2:32 PM, Grant Likely wrote: > On Tue, Nov 20, 2012 at 10:23 PM, Simon Glass wrote: >> Hi, >> >> I hope this is a stupid question with an easy answer, but I cannot find it. >> >> I have a device tree node for an mmc block device and I want to use >> that block device from another driver. I have a phandle which lets me >> get the node of the mmc device, but I am not sure how to convert that >> into a block_device. In order to do so, I think I need a major/minor >> number. Of course the phandle might in fact point to a SCSI driver and >> I want that to work correctly also. >> >> I imagine I might be able to search through the wonders of sysfs in >> user space, but is there a better way? > > Do you /want/ to do it from userspace? What is your use case? Mounting > the rootfs? The use case is storing some raw data on a block device from within a driver in the kernel. It is used to keep track of the verified boot state. > > Regardless, userspace can monitor the uevents when devices are added > (that's what udev does) and watch for the full path of the node you > want in the uevent attribute. Then you can look for the child device > with the block major/minor numbers in it. So is there a way to do this entirely in the kernel ex post? It might need to happen during kernel boot, before user space. > > g. Thanks, Simon