From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757304Ab2IQWDr (ORCPT ); Mon, 17 Sep 2012 18:03:47 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:34619 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753440Ab2IQWDq (ORCPT ); Mon, 17 Sep 2012 18:03:46 -0400 Date: Mon, 17 Sep 2012 23:03:34 +0100 From: Russell King - ARM Linux To: Arnd Bergmann Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Will Deacon , Nicolas Pitre , "James E.J. Bottomley" , linux-scsi@vger.kernel.org Subject: Re: [PATCH 22/24] scsi: eesox: use __iomem pointers for MMIO Message-ID: <20120917220334.GU12245@n2100.arm.linux.org.uk> References: <201209150800.35605.arnd@arndb.de> <20120915085734.GG12245@n2100.arm.linux.org.uk> <201209151030.44105.arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201209151030.44105.arnd@arndb.de> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Sep 15, 2012 at 10:30:43AM +0000, Arnd Bergmann wrote: > On Saturday 15 September 2012, Russell King - ARM Linux wrote: > > On Sat, Sep 15, 2012 at 08:00:35AM +0000, Arnd Bergmann wrote: > > > On Friday 14 September 2012, Russell King - ARM Linux wrote: > > > > On Fri, Sep 14, 2012 at 11:34:50PM +0200, Arnd Bergmann wrote: > > > > > ARM is moving to stricter checks on readl/write functions, > > > > > so we need to use the correct types everywhere. > > > > > > > > There's nothing wrong with const iomem pointers. If you think > > > > otherwise, patch x86 not to use const in its accessor implementation > > > > and watch the reaction: > > > > > > > > #define build_mmio_read(name, size, type, reg, barrier) \ > > > > static inline type name(const volatile void __iomem *addr) \ > > > > { type ret; asm volatile("mov" size " %1,%0":reg (ret) \ > > > > :"m" (*(volatile type __force *)addr) barrier); return ret; } > > > > > > > > build_mmio_read(readb, "b", unsigned char, "=q", :"memory") > > > > build_mmio_read(readw, "w", unsigned short, "=r", :"memory") > > > > build_mmio_read(readl, "l", unsigned int, "=r", :"memory") > > > > > > Ok, fair enough. Can you fold the patch below into > > > "ARM: 7500/1: io: avoid writeback addressing modes for __raw_ > > > accessors", or apply on top then? > > > > No - const is not appropriate for the write accessors. Again, this puts > > us at odds with x86: > > > > #define build_mmio_write(name, size, type, reg, barrier) \ > > static inline void name(type val, volatile void __iomem *addr) \ > > { asm volatile("mov" size " %0,%1": :reg (val), \ > > "m" (*(volatile type __force *)addr) barrier); } > > > > build_mmio_write(writeb, "b", unsigned char, "q", :"memory") > > build_mmio_write(writew, "w", unsigned short, "r", :"memory") > > build_mmio_write(writel, "l", unsigned int, "r", :"memory") > > > > So, readl etc are all const volatile void __iomem *, but writel etc are > > all volatile void __iomem *. > > > > How they're defined on ARM after 7500/1 copies how they're defined on > > x86. > > Well, you have to make up your mind what you want. Right now, we get these > warnings in rpc_defconfig: > > Generating include/generated/mach-types.h > /home/arnd/linux-arm/drivers/net/ethernet/seeq/ether3.c: In function 'ether3_outb': > /home/arnd/linux-arm/drivers/net/ethernet/seeq/ether3.c:104:2: error: passing argument 2 of '__raw_writeb' discards 'const' qualifier from pointer target type [-Werror] > /home/arnd/linux-arm/arch/arm/include/asm/io.h:81:91: note: expected 'volatile void *' but argument is of type 'const void *' > /home/arnd/linux-arm/drivers/scsi/arm/eesox.c: In function 'eesoxscsi_buffer_out': > /home/arnd/linux-arm/drivers/scsi/arm/eesox.c:310:4: error: passing argument 2 of '__raw_writel' discards 'const' qualifier from pointer target type [-Werror] > /home/arnd/linux-arm/arch/arm/include/asm/io.h:88:91: note: expected 'volatile void *' but argument is of type 'const void *' > /home/arnd/linux-arm/drivers/scsi/arm/eesox.c:324:4: error: passing argument 2 of '__raw_writel' discards 'const' qualifier from pointer target type [-Werror] > /home/arnd/linux-arm/arch/arm/include/asm/io.h:88:91: note: expected 'volatile void *' but argument is of type 'const void *' > /home/arnd/linux-arm/drivers/scsi/arm/eesox.c:325:4: error: passing argument 2 of '__raw_writel' discards 'const' qualifier from pointer target type [-Werror] > /home/arnd/linux-arm/arch/arm/include/asm/io.h:88:91: note: expected 'volatile void *' but argument is of type 'const void *' > > Either we allow drivers to write to const __iomem pointers or we don't. I > don't care which way we do it, but just saying both patches are wrong is > not very helpful. In both of my replies, I've said "as x86 does". We need to follow x86's behaviour here, which is as I've quoted - it's not a matter that "I need to make up my mind" - my mind is already well made up. That is, we need to follow x86 here. That is, const volatile void __iomem * for reads, and volatile void __iomem * for writes.