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[72.189.64.225]) by smtp.gmail.com with ESMTPSA id n124sm2004093qkn.24.2020.05.05.07.54.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 May 2020 07:54:09 -0700 (PDT) Date: Tue, 5 May 2020 10:53:49 -0400 From: William Breathitt Gray To: Andy Shevchenko , Linus Walleij , Bartosz Golaszewski , Michal Simek Cc: Andy Shevchenko , Syed Nayyar Waris , Andrew Morton , Arnd Bergmann , rrichter@marvell.com, Bartosz Golaszewski , Masahiro Yamada , "Zhang, Rui" , Daniel Lezcano , Amit Kucheria , Linux-Arch , "open list:GPIO SUBSYSTEM" , Linux Kernel Mailing List , linux-arm Mailing List , Linux PM Subject: Re: [PATCH v5 0/4] Introduce the for_each_set_clump macro Message-ID: <20200505145250.GA5979@shinobu> References: <20200504114109.GE185537@smile.fi.intel.com> <20200504143638.GA4635@shinobu> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="CblX+4bnyfN0pR09" Content-Disposition: inline In-Reply-To: Sender: linux-gpio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org --CblX+4bnyfN0pR09 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, May 05, 2020 at 04:51:56PM +0300, Andy Shevchenko wrote: > On Mon, May 4, 2020 at 5:41 PM William Breathitt Gray > wrote: > > On Mon, May 04, 2020 at 02:41:09PM +0300, Andy Shevchenko wrote: > > > On Sun, May 03, 2020 at 04:38:36AM +0530, Syed Nayyar Waris wrote: >=20 > ... >=20 > > > Looking into the last patches where we have examples I still do not s= ee a > > > benefit of variadic clump sizes. power of 2 sizes would make sense (a= nd be > > > optimized accordingly (64-bit, 32-bit). > > > > > > -- > > > With Best Regards, > > > Andy Shevchenko > > > > There is of course benefit in defining for_each_set_clump with clump > > sizes of powers of 2 (we can optimize for 32 and 64 bit sizes and avoid > > boundary checks that we know will not occur), but at the very least the > > variable size bitmap_set_value and bitmap_get_value provide significant > > benefit for the readability of the gpio-xilinx code: > > > > bitmap_set_value(old, state[0], 0, width[0]); > > bitmap_set_value(old, state[1], width[0], width[1]); > > ... > > state[0] =3D bitmap_get_value(new, 0, width[0]); > > state[1] =3D bitmap_get_value(new, width[0], width[1]); > > > > These lines are simple and clear to read: we know immediately what they > > do. But if we did not have bitmap_set_value/bitmap_get_value, we'd have > > to use several bitwise operations for each line; the obfuscation of the > > code would be an obvious hinderance here. >=20 > Do I understand correctly that width[0] and width[1] may not be power > of two and it's actually the case? >=20 > --=20 > With Best Regards, > Andy Shevchenko I'm under the impression that width[0] and width[1] are arbitrarily chosen by the user and could be any integer. I have never used this hardware so I'm hoping one of the gpio-xilinx or GPIO subsystem maintainers in this thread will respond with some guidance. If the values of width[0] and width[1] are restricted to powers of 2, then I agree that there is no need for generic bitmap_set_value and bitmap_get_value functions and we can instead use more optimized power of 2 versions. 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