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Message-ID: <20211123153933.49ff8b72@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 23 Nov 2021 15:39:33 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Johannes Berg <johannes@...solutions.net>,
        Tony Lindgren <tony@...mide.com>,
        Russell King <linux@...linux.org.uk>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Paul Walmsley <paul@...an.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        Tero Kristo <kristo@...nel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Lorenzo Bianconi <lorenzo.bianconi83@...il.com>,
        Benoit Parrot <bparrot@...com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Andrew Jeffery <andrew@...id.au>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Joel Stanley <joel@....id.au>,
        Ping-Ke Shih <pkshih@...ltek.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S . Miller" <davem@...emloft.net>,
        Linus Walleij <linus.walleij@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Magnus Damm <magnus.damm@...il.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Keerthy <j-keerthy@...com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Kucheria <amitk@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-media@...r.kernel.org, linux-mmc@...r.kernel.org,
        linux-aspeed@...ts.ozlabs.org, openbmc@...ts.ozlabs.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-pm@...r.kernel.org,
        alsa-devel@...a-project.org
Subject: Re: [PATCH 01/17] bitfield: Add non-constant field_{prep,get}()
 helpers

On Tue, 23 Nov 2021 09:36:22 +0100 Geert Uytterhoeven wrote:
> > > Also, you're using __ffs(), which doesn't work for 64-bit on 32-bit
> > > architectures (afaict), so that seems a bit awkward.
> > >
> > > Maybe we can make {u32,...}_get_bits() be doing compile-time only checks
> > > if it is indeed a constant? The __field_overflow() usage is already only
> > > done if __builtin_constant_p(v), so I guess we can do the same with
> > > __bad_mask()?  
> >
> > Either that or add decomposition macros. Are compilers still really bad
> > at passing small structs by value?  
> 
> Sorry, I don't get what you mean by adding decomposition macros.
> Can you please elaborate?

#define DECOMPOSE(_mask) \
  (struct bf){ .mask = _mask, .shf = __bf_shf(_mask), }

Then drivers can save or pass around the mask and shift params 
broken apart as a small struct.

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