From mboxrd@z Thu Jan 1 00:00:00 1970 From: Janusz Krzysztofik Subject: Re: [RFC PATCH v2 09/12] gpiolib: Identify GPIO descriptor arrays with direct mapping Date: Tue, 07 Aug 2018 18:50:22 +0200 Message-ID: <1793769.2WP40jSPqy@z50> References: <20180718235710.18242-1-jmkrzyszt@gmail.com> <20180806222918.12644-10-jmkrzyszt@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Linus Walleij Cc: Boris Brezillon , Jonathan Corbet , =?ISO-8859-1?Q?Miqu=E8l?= 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" , Janusz Krzysztofik List-Id: linux-gpio@vger.kernel.org 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? Thanks, Janusz