From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.0 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 2B04C7E3B8 for ; Tue, 7 Aug 2018 17:11:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390107AbeHGT0Z (ORCPT ); Tue, 7 Aug 2018 15:26:25 -0400 Received: from mail.bootlin.com ([62.4.15.54]:36790 "EHLO mail.bootlin.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388706AbeHGT0Z (ORCPT ); Tue, 7 Aug 2018 15:26:25 -0400 Received: by mail.bootlin.com (Postfix, from userid 110) id CD33320789; Tue, 7 Aug 2018 19:11:04 +0200 (CEST) Received: from bbrezillon (91-160-177-164.subs.proxad.net [91.160.177.164]) by mail.bootlin.com (Postfix) with ESMTPSA id 1C5A02093C; Tue, 7 Aug 2018 19:10:42 +0200 (CEST) Date: Tue, 7 Aug 2018 19:10:42 +0200 From: Boris Brezillon To: Janusz Krzysztofik Cc: Linus Walleij , Jonathan Corbet , =?UTF-8?B?TWlxdcOobA==?= Raynal , Richard Weinberger , David Woodhouse , Brian Norris , Mark Vasut , ext Tony Lindgren , Aaro Koskinen , Linux ARM , Linux-OMAP , linux-mtd@lists.infradead.org, linux-doc@vger.kernel.org, "open list:GPIO SUBSYSTEM" , "linux-kernel@vger.kernel.org" Subject: Re: [RFC PATCH v2 09/12] gpiolib: Identify GPIO descriptor arrays with direct mapping Message-ID: <20180807191042.0204909a@bbrezillon> In-Reply-To: <1793769.2WP40jSPqy@z50> References: <20180718235710.18242-1-jmkrzyszt@gmail.com> <20180806222918.12644-10-jmkrzyszt@gmail.com> <1793769.2WP40jSPqy@z50> X-Mailer: Claws Mail 3.15.0-dirty (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Tue, 07 Aug 2018 18:50:22 +0200 Janusz Krzysztofik wrote: > Hi Linus, > > On Tuesday, August 7, 2018 1:29:43 AM CEST Linus Walleij wrote: > > Hi Janusz! > > > > On Tue, Aug 7, 2018 at 12:29 AM Janusz Krzysztofik > wrote: > > > > > Certain GPIO array lookup results may map directly to GPIO pins of a > > > single GPIO chip in hardware order. If that condition is recognized > > > and handled efficiently, significant performance gain of get/set array > > > functions may be possible. > > > > > > While processing a request for an array of GPIO descriptors, verify if > > > the descriptors just collected represent consecutive pins of a single > > > GPIO chip. Pass that information with the array to the caller so it > > > can benefit from enhanced performance as soon as bitmap based get/set > > > array functions which can make efficient use of that are available. > > > > > > Signed-off-by: Janusz Krzysztofik > > (...) > > > This function returns a struct gpio_descs which contains an array of > > > -descriptors:: > > > +descriptors. It may also contain a valid descriptor of a single GPIO > chip in > > > +case the array strictly matches pin hardware layout of the chip:: > > > > > > struct gpio_descs { > > > unsigned int ndescs; > > > struct gpio_desc *desc[]; > > > + struct gpio_chip *chip; > > > > This must be motivated: if the only purpose is to indicate to the consumer > that > > all GPIOs are on the same chip, why not just have a > > > > bool all_on_same_chip; > > > > That you set to true if these are all on the same chip? > > My approach would probably save one or two instructions per get/set call, but > I'm not stuck to it and will be happy to find a better solution. > > How about folding the chip descriptor inside an additional structure, private > to drivers, with internals not revealed to consumers? Or just get the chip from gpio_descs->desc[0]->gdev->chip when ->all_on_same_chip is true... That adds 2 dereferencing though. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html