From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1B039C4360C for ; Thu, 10 Oct 2019 08:21:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EA2EA2067B for ; Thu, 10 Oct 2019 08:21:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733271AbfJJIV6 (ORCPT ); Thu, 10 Oct 2019 04:21:58 -0400 Received: from mail-oi1-f195.google.com ([209.85.167.195]:36118 "EHLO mail-oi1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733269AbfJJIV6 (ORCPT ); Thu, 10 Oct 2019 04:21:58 -0400 Received: by mail-oi1-f195.google.com with SMTP id k20so4177793oih.3; Thu, 10 Oct 2019 01:21:57 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=dc5RA2BPKZVYGXJLYtKKxLVdHq6Dac4u37aEDEUkLQM=; b=DHfArRrkuDjQXYob8Lw47pqT7FpGLO3GzFoGIG4uahhSnTK01APmr63DFxVyPUMF9M 3KekuOiGOLQGQlsHJPINfnYMaEoO8oH7vvDSQ3D782Eu6QJIzQw+ZOESPV165k1suM/q mCdDvgFn+N0YWjiOO4vd5HUQbEB0dtvmpES5TLEoCGNSc8ALolmKN+AgmzyzeiYTCYwx qBmmg6x3JMY9fy5oh6/4I38nDvR2DSakyqXIg091/+7T6cEulp95VbPTY1oxPC5Ulmvf FDXcVa96udIjaf9nWPrv6JUBXiq6yXBqdxqWAk5WxCZ9VCsMzjeplrVSKMkaNISJA5wU cgZw== X-Gm-Message-State: APjAAAXhxIECF093MrNyvztttwiNc+b31SFLnrqLH48n+NJfQSb6E56L a9xoCW8l/YiZQsc6h1HiDgQm9G+i20VvtnUFiv0= X-Google-Smtp-Source: APXvYqxtgx03+B0HB6RKN9jHyeCpS8CcGrjyRFWnknFz7FyEGnnntki6sJN+xgX/b9Aj5CRhCziqQeixZ7YTrOe0LG8= X-Received: by 2002:aca:4bd2:: with SMTP id y201mr6665365oia.102.1570695716750; Thu, 10 Oct 2019 01:21:56 -0700 (PDT) MIME-Version: 1.0 References: <893c3b4f03266c9496137cc98ac2b1bd27f92c73.1570633189.git.vilhelm.gray@gmail.com> <20191009170917.GG32742@smile.fi.intel.com> <20191010080750.GN32742@smile.fi.intel.com> In-Reply-To: <20191010080750.GN32742@smile.fi.intel.com> From: Geert Uytterhoeven Date: Thu, 10 Oct 2019 10:21:45 +0200 Message-ID: Subject: Re: [PATCH v17 01/14] bitops: Introduce the for_each_set_clump8 macro To: Andy Shevchenko Cc: Masahiro Yamada , William Breathitt Gray , Linus Walleij , Bartosz Golaszewski , Andrew Morton , "open list:GPIO SUBSYSTEM" , Linux Kernel Mailing List , linux-arch , Rasmus Villemoes , linux-arm-kernel , Linux PM mailing list , Phil Reid , Lukas Wunner , sean.nyekjaer@prevas.dk, morten.tiljeset@prevas.dk, Arnd Bergmann Content-Type: text/plain; charset="UTF-8" Sender: linux-gpio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org Hi Andy, On Thu, Oct 10, 2019 at 10:08 AM Andy Shevchenko wrote: > On Thu, Oct 10, 2019 at 09:49:51AM +0200, Geert Uytterhoeven wrote: > > On Thu, Oct 10, 2019 at 9:42 AM Andy Shevchenko > > wrote: > > > On Thu, Oct 10, 2019 at 9:29 AM Geert Uytterhoeven wrote: > > > > On Thu, Oct 10, 2019 at 7:49 AM Andy Shevchenko > > > > wrote: > > > > > On Thu, Oct 10, 2019 at 5:31 AM Masahiro Yamada > > > > > wrote: > > > > > > On Thu, Oct 10, 2019 at 3:54 AM Geert Uytterhoeven wrote: > > > > > > > On Wed, Oct 9, 2019 at 7:09 PM Andy Shevchenko > > > > > > > wrote: > > > > > > > > On Thu, Oct 10, 2019 at 01:28:08AM +0900, Masahiro Yamada wrote: > > > > > > > > > On Thu, Oct 10, 2019 at 12:27 AM William Breathitt Gray > > > > > > > > > wrote: > > > > > > > > > > Why is the return type "unsigned long" where you know > > > > > > > > > it return the 8-bit value ? > > > > > > > > > > > > > > > > Because bitmap API operates on unsigned long type. This is not only > > > > > > > > consistency, but for sake of flexibility in case we would like to introduce > > > > > > > > more calls like clump16 or so. > > > > > > > > > > > > > > TBH, that doesn't convince me: those functions explicitly take/return an > > > > > > > 8-bit value, and have "8" in their name. The 8-bit value is never > > > > > > > really related to, retrieved from, or stored in a full "unsigned long" > > > > > > > element of a bitmap, only to/from/in a part (byte) of it. > > > > > > > > > > > > > > Following your rationale, all of iowrite{8,16,32,64}*() should take an > > > > > > > "unsigned long" value, too. > > > > > > > > > > > > Using u8/u16/u32/u64 looks more consistent with other bitmap helpers. > > > > > > > > > > > > void bitmap_from_arr32(unsigned long *bitmap, const u32 *buf, unsigned > > > > > > int nbits); > > > > > > void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, unsigned int nbits); > > > > > > static inline void bitmap_from_u64(unsigned long *dst, u64 mask); > > > > > > > > > > > > If you want to see more examples from other parts, > > > > > > > > > > Geert's and yours examples both are not related. They are about > > > > > fixed-width properies when we know that is the part of protocol. > > > > > Here we have no protocol which stricts us to the mentioned fixed-width types. > > > > > > > > Yes you have: they are functions to store/retrieve an 8-bit value from > > > > the middle of the bitmap, which is reflected in their names ("clump8", > > > > "value8"). > > > > The input/output value is clearly separated from the actual bitmap, > > > > which is referenced by the "unsigned long *". > > > > > > > > If you add new "value16" functions, they will be intended to store/retrieve > > > > 16-bit values. > > > > > > And if I add 4-bit, 12-bit or 24-bit values, what should I use? > > > > Whatever is needed to store that? > > I agree "unsigned long" is appropriate for a generic function to extract a > > bit field of 1 to BITS_PER_LONG bits. > > > > > > Besides, if retrieving an 8-bit value requires passing an > > > > "unsigned long *", the caller needs two variables: one unsigned long to > > > > pass the address of, and one u8 to copy the returned value into. > > > > > > Why do you need a temporary variable? In some cases it might make > > > sense, but in general simple cases I don't see what you may achieve > > > with it. > > > > Because find_next_clump8() takes a pointer to store the output value. > > So does regmap_read(). I believe that one is different, as it is a generic function, and the width of the returned value depends on the regmap config. > 8 appeared there during review when it has been proposed to optimize to 8-bit > clumps as most of the current users utilize it. The initial idea was to be > bit-width agnostic. And with current API it's possible to easy convert to other > formats later if we need. "optimized for 8-bit clumps" and "out-of-line function that takes an unsigned long pointer for an output parameter" don't match well, IMHO. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds