Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964846Ab2KUUsM (ORCPT ); Wed, 21 Nov 2012 15:48:12 -0500 Received: from mail-oa0-f46.google.com ([209.85.219.46]:42715 "EHLO mail-oa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964771Ab2KUUsK (ORCPT ); Wed, 21 Nov 2012 15:48:10 -0500 MIME-Version: 1.0 In-Reply-To: <20121121154758.93CE43E0AE2@localhost> References: <20121121154758.93CE43E0AE2@localhost> Date: Wed, 21 Nov 2012 12:48:09 -0800 X-Google-Sender-Auth: jVuChRjQpgiomrlOFwlOLSbHlno 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 Content-Length: 2697 Lines: 63 Hi Grant, On Wed, Nov 21, 2012 at 7:47 AM, Grant Likely wrote: > 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. OK thank you. Was hoping to find a simple way to find a block device from a device tree node (yes I know the right one) but I suppose in general this is impossible, since nodes may create more than one device, and each has its own data structures leading to the block device. So it seems like a notifier is the best way. Thanks for looking at this Grant. Regards, Simon > > g. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/