From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH] asm-generic/io.h: Implement read[bwlq]_relaxed() Date: Tue, 9 Sep 2014 13:28:18 +0100 Message-ID: <20140909122818.GI1754@arm.com> References: <1410264760-29756-1-git-send-email-daniel.thompson@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:42073 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756065AbaIIM2b (ORCPT ); Tue, 9 Sep 2014 08:28:31 -0400 Content-Disposition: inline In-Reply-To: <1410264760-29756-1-git-send-email-daniel.thompson@linaro.org> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Daniel Thompson Cc: Arnd Bergmann , "linux-kernel@vger.kernel.org" , "patches@linaro.org" , "linaro-kernel@lists.linaro.org" , "linux-arch@vger.kernel.org" Hi Daniel, On Tue, Sep 09, 2014 at 01:12:40PM +0100, Daniel Thompson wrote: > Currently the read[bwlq]_relaxed() family are implemented on every > architecture except blackfin, m68k[1], metag, openrisc, s390[2] and > score. Increasingly drivers are being optimized to exploit relaxed > reads putting these architectures at risk of compilation failures for > shared drivers. > > This patch addresses this by providing implementations of > read[bwlq]_relaxed() that are identical to the equivalent read[bwlq](). > All the above architectures include asm-generic/io.h . > > Note that currently only eight architectures (alpha, arm, arm64, avr32, > hexagon, microblaze, mips and sh) implement write[bwlq]_relaxed() meaning > these functions are deliberately not included in this patch. > > [1] m68k includes the relaxed family only when configured *without* MMU. > [2] s390 requires CONFIG_PCI to include the relaxed family. > > Signed-off-by: Daniel Thompson > Cc: Will Deacon > Cc: Arnd Bergmann > Cc: linux-arch@vger.kernel.org > --- > include/asm-generic/io.h | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) I have a larger series adding these (and the write equivalents) to all architectures that I periodically post and then fail to get on top of. The key part you're missing is defining some generic semantics for these accessors. Without those, I don't think it makes sense to put them into asm-generic, because drivers can't safely infer any meaning from the relaxed definition. Ben and I agreed on something back in May: https://lkml.org/lkml/2014/5/22/468 but I need to send a new version including: - ioreadX_relaxed and iowriteX_relaxed - Strengthening non-relaxed I/O accessors on architectures with non-empty mmiowb() I'll bump it up the list. In the meantime, you can have a look at my io branch on kernel.org Will