From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754171Ab2KLXQ3 (ORCPT ); Mon, 12 Nov 2012 18:16:29 -0500 Received: from mail-wg0-f44.google.com ([74.125.82.44]:34096 "EHLO mail-wg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753209Ab2KLXQ2 (ORCPT ); Mon, 12 Nov 2012 18:16:28 -0500 MIME-Version: 1.0 In-Reply-To: References: From: Bjorn Helgaas Date: Mon, 12 Nov 2012 16:16:06 -0700 Message-ID: Subject: Re: Q: Kconfig option VIRT_TO_BUS To: H Hartley Sweeten Cc: "linux-kernel@vger.kernel.org" , Stephen Rothwell 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 On Mon, Nov 12, 2012 at 4:13 PM, H Hartley Sweeten wrote: > On Monday, November 12, 2012 11:41 AM, Bjorn Helgaas wrote: >> On Mon, Nov 12, 2012 at 9:18 AM, H Hartley Sweeten wrote: >>> Does anyone know what the Kconfig option VIRT_TO_BUS does? >>> There are a number of "depends on" that option but it does not >>> seem to directly enable any code in the kernel. >> >> virt_to_bus() is a deprecated interface for converting a kernel >> virtual address to a bus address. It's deprecated because it's >> impossible to implement correctly when there are multiple bus address >> spaces, because you don't know which bus address space the caller has >> in mind. > > Thanks for the info. > > So if a driver does not use virt_to_bus() then the "depends on VIRT_TO_BUS" > is not necessary. Correct? Yes, that's my understanding.