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Date:   Fri, 24 Apr 2020 12:42:00 -0400
From:   William Breathitt Gray <vilhelm.gray@gmail.com>
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc:     Lukas Wunner <lukas@wunner.de>,
        Syed Nayyar Waris <syednwaris@gmail.com>,
        akpm@linux-foundation.org, arnd@arndb.de,
        Linus Walleij <linus.walleij@linaro.org>,
        linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/6] bitops: Introduce the the for_each_set_clump macro
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On Fri, Apr 24, 2020 at 07:34:10PM +0300, Andy Shevchenko wrote:
> On Fri, Apr 24, 2020 at 11:09:26AM -0400, William Breathitt Gray wrote:
> > On Fri, Apr 24, 2020 at 05:00:58PM +0200, Lukas Wunner wrote:
> > > On Fri, Apr 24, 2020 at 08:22:38PM +0530, Syed Nayyar Waris wrote:
> > > > On Fri, Apr 24, 2020 at 7:40 PM Lukas Wunner <lukas@wunner.de> wrot=
e:
> > > > > On Fri, Apr 24, 2020 at 05:55:21PM +0530, Syed Nayyar Waris wrote:
>=20
> ...
>=20
> > > > So, this function preserves the behaviour of earlier
> > > > bitmap_set_value8() function and also adds extra functionality to
> > > > that.
> > >=20
> > > Please leave drivers as is which use exclusively 8-bit accesses,
> > > e.g. gpio-max3191x.c and gpio-74x164.c.  I'm fearing a performance
> > > regression if your new generic variant is used.  They work perfectly
> > > fine the way they are and I don't see any benefit this series may have
> > > for them.
> > >=20
> > > If there are other drivers which benefit from the flexibility of your
> > > generic variant then I'm not opposed to changing those.
>=20
> > We can leave of course bitmap_set_value8 alone, but for 8-bit values the
> > difference in latency I suspect is primarily due to the conditional test
> > for the word boundaries. This latency is surely overshadowed by the I/O
> > latency of the GPIO drivers, so I don't think there's much harm in
> > changing those to use the generic function when the bottleneck will not
> > be due to the bitmap_set_value/bitmap_get_value operations.
>=20
> Okay, how many new (non-8-bit) users this will target?
>=20
> --=20
> With Best Regards,
> Andy Shevchenko

Within this patchset the only non-8-bit users are gpio-thunderx and
gpio-xilinix. The gpio-xilinx has configurable port widths so in some
instances it can behave like the 8-bit users, but not always.

If you want to keep the existing for_each_set_clump8 and related
functions, ignore [PATCH 3/6] and [PATCH 4/6]. That should allow this
patchset to be just an introduction of the new generic functions without
affecting the existing 8-bit users.

William Breathitt Gray

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