From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755266Ab2KUPsJ (ORCPT ); Wed, 21 Nov 2012 10:48:09 -0500 Received: from mail-we0-f174.google.com ([74.125.82.174]:57566 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755169Ab2KUPsG (ORCPT ); Wed, 21 Nov 2012 10:48:06 -0500 From: Grant Likely Subject: Re: Device tree node to major/minor? To: Simon Glass Cc: lk , Devicetree Discuss , Che-liang Chiou In-Reply-To: References: Date: Wed, 21 Nov 2012 15:47:58 +0000 Message-Id: <20121121154758.93CE43E0AE2@localhost> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 20 Nov 2012 15:48:24 -0800, Simon Glass wrote: > 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. Yes, it is certainly doable within the kernel. First, you'll need to use a notifier to get called back whenever a new device is created. Then you'll need to look at the dev->of_node(->full_name) to see if it is the node you actually want. You might need/want to resolve it from an alias or something, but I presume you already have a way to find the device_node before seaching for a struct device. g.