From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: [PATCH 01/11] irqchip: Allow irq_reg_{readl,writel} to use __raw_{readl_writel} Date: Wed, 29 Oct 2014 22:31:06 +0100 (CET) Message-ID: References: <1414555138-6500-1-git-send-email-cernekee@gmail.com> <5338153.4SY4TFtus9@wuerfel> <22478002.kqKBdeLAKz@wuerfel> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Return-path: In-Reply-To: <22478002.kqKBdeLAKz@wuerfel> Sender: linux-kernel-owner@vger.kernel.org To: Arnd Bergmann Cc: Kevin Cernekee , Florian Fainelli , Jason Cooper , Ralf Baechle , "linux-kernel@vger.kernel.org" , "devicetree@vger.kernel.org" , Maxime Bizon , Jonas Gorski , Linux MIPS Mailing List List-Id: devicetree@vger.kernel.org On Wed, 29 Oct 2014, Arnd Bergmann wrote: > On Wednesday 29 October 2014 13:09:47 Kevin Cernekee wrote: > > generic-chip.c already has a fair amount of indirection, with pointers > > to saved masks, user-specified register offsets, and such. Is there a > > concern that introducing, say, a pair of readl/writel function > > pointers, would cause an unacceptable performance drop? > > I don't know. Thomas' reply suggests that it isn't. Doing byteswap > in software at a register access is usually free in terms of CPU > cycles, but an indirect function call can be noticeable if we do > that a lot. I did not say that it is free. I merily said that I prefer to have this solved at the core level rather than at the driver level. So you have several options to do so: 1) Indirections 2) Different functions for the different access modes 3) Alternatives #1 Is the simplest solution, but imposes the overhead of an indirect function call for something trivial #2 The most efficient and flexible way if you have to provide different access modes for different drivers. But it comes with the price of increasing the text foot print. #3 Smart and efficient, but requires that on a particular system all drivers use the same access mode. Thanks, tglx