From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40B19k5k1TzF2Cp for ; Wed, 28 Mar 2018 19:23:36 +1100 (AEDT) Message-ID: <1522222979.7364.118.camel@kernel.crashing.org> Subject: Re: RFC on writel and writel_relaxed From: Benjamin Herrenschmidt To: Arnd Bergmann Cc: Linus Torvalds , Alexander Duyck , Will Deacon , Sinan Kaya , Jason Gunthorpe , David Laight , Oliver , "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" , "linux-rdma@vger.kernel.org" , "Paul E. McKenney" , "netdev@vger.kernel.org" Date: Wed, 28 Mar 2018 18:42:59 +1100 In-Reply-To: References: <1521854626.16434.359.camel@kernel.crashing.org> <58ce5b83f40f4775bec1be8db66adb0d@AcuMS.aculab.com> <20180326165425.GA15554@ziepe.ca> <20180326202545.GB15554@ziepe.ca> <20180326210951.GD15554@ziepe.ca> <1522101616.7364.13.camel@kernel.crashing.org> <1e077f6a-90b6-cce9-6f0f-a8c003fec850@codeaurora.org> <20180327151029.GB17494@arm.com> <1522186396.7364.61.camel@kernel.crashing.org> <1522198981.7364.81.camel@kernel.crashing.org> <1522211620.7364.94.camel@kernel.crashing.org> <1522219376.7364.109.camel@kernel.crashing.org> <1522220165.7364.110.camel@kernel.crashing.org> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 2018-03-28 at 09:11 +0200, Arnd Bergmann wrote: > On Wed, Mar 28, 2018 at 8:56 AM, Benjamin Herrenschmidt > wrote: > > On Wed, 2018-03-28 at 06:53 +0000, Linus Torvalds wrote: > > > On Tue, Mar 27, 2018, 20:43 Benjamin Herrenschmidt wrote: > > > That's why in/out were *so* slow, and why nobody uses them any more > > > (well, the address size limitations and the lack of any remapping of > > > the address obviously also are a reason). > > > > All true indeed, though a lot of other archs never quite made them > > fully synchronous, which was another can of worms ... oh well. > > Many architectures have no way of providing PCI compliant semantics > for outb, as their instruction set and/or bus interconnect lacks a > method of waiting for completion of an outb. Yup, that includes powerpc. Note that since POWER8 we don't even genetate IO space anymore :-) > In practice, it doesn't seem to matter for any of the devices one would > encounter these days: very few use I/O space, and those that do don't > actually rely on the strict ordering. Some architectures (in particular > s390, but I remember seeing the same thing elsewhere) explicitly > disallow I/O space access on PCI because of this. On ARM, the typical > PCI implementations have other problems that are worse than this > one, so most drivers are fine with the almost-working semantics. /me cries... Ben.