From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933733AbbJHPBf (ORCPT ); Thu, 8 Oct 2015 11:01:35 -0400 Received: from pandora.arm.linux.org.uk ([78.32.30.218]:48133 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753932AbbJHPBd (ORCPT ); Thu, 8 Oct 2015 11:01:33 -0400 Date: Thu, 8 Oct 2015 16:01:21 +0100 From: Russell King - ARM Linux To: Andre Przywara Cc: Alexandre Belloni , Greg Kroah-Hartman , Jiri Slaby , Nicolas Ferre , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] serial: atmel: fix compiler warning on address cast Message-ID: <20151008150120.GF32532@n2100.arm.linux.org.uk> References: <1444064452-12285-1-git-send-email-andre.przywara@arm.com> <20151008090148.GE3485@piout.net> <20151008093749.GB32532@n2100.arm.linux.org.uk> <20151008103835.GF3485@piout.net> <56168292.5030207@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56168292.5030207@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 08, 2015 at 03:49:54PM +0100, Andre Przywara wrote: > Hi, > > On 08/10/15 11:38, Alexandre Belloni wrote: > > On 08/10/2015 at 10:37:49 +0100, Russell King - ARM Linux wrote : > >> On Thu, Oct 08, 2015 at 11:01:48AM +0200, Alexandre Belloni wrote: > >>> On 05/10/2015 at 18:00:52 +0100, Andre Przywara wrote : > >>>> Turning on KVM and LPAE support on top of a multi_v7_defconfig will > >>>> produce a compiler warning in the Atmel serial driver: > >>>> drivers/tty/serial/atmel_serial.c: In function 'atmel_verify_port': > >>>> drivers/tty/serial/atmel_serial.c:2299:6: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast] > >>>> if ((void *)port->mapbase != ser->iomem_base) > >>>> ^ > >>>> > >>>> Fix that by using the cast on the right hand side instead, as similar > >>>> code already does in other drivers. > >>>> > >>>> Signed-off-by: Andre Przywara > >>> Acked-by: Alexandre Belloni > >> > >> Hmm, this actually points at a problem, and the cast screems out about it. > >> Think about it, can you guess what it is? > > Russell, I'd really appreciate if we wouldn't have to play > "guess-what-I-am-thinking" here. Can't you just say what's bothering you? Actually, I think it's fine - the interface is just another one of the weird cases we have in the kernel. However, for the record, things get typed a certain way for a reason. Virtual addresses that can be dereferenced are generally pointer like. Physical addresses are generally integers. Casting between the two generally indicates a bug, and whenever you see a cast between the two, it should have special attention paid to it to make sure that it really is correct. There are a few famous places in the kernel where casting between an unsigned long and a virtual address is pretty standard, but they're the exception to the rule (eg, the argument to a timer, get_free_page()). This is another example. Sorry for creating confusion. -- FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.