linux-kernel - Re: [PATCH 2/5] include: add setbits32/clrbits32/clrsetbits32/setbits64/clrbits64/clrsetbits64 in linux/setbits.h

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Date:   Mon, 10 Sep 2018 20:49:29 +0200
From:   LABBE Corentin <clabbe@...libre.com>
To:     Scott Wood <oss@...error.net>
Cc:     Gilles.Muller@...6.fr, Julia.Lawall@...6.fr, agust@...x.de,
        alexandre.torgue@...com, alistair@...ple.id.au,
        benh@...nel.crashing.org, carlo@...one.org, davem@...emloft.net,
        galak@...nel.crashing.org, joabreu@...opsys.com,
        khilman@...libre.com, maxime.ripard@...tlin.com,
        michal.lkml@...kovi.net, mpe@...erman.id.au,
        mporter@...nel.crashing.org, nicolas.palix@...g.fr,
        paulus@...ba.org, peppe.cavallaro@...com, tj@...nel.org,
        vitb@...nel.crashing.org, wens@...e.org, cocci@...teme.lip6.fr,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-ide@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        netdev@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH 2/5] include: add
 setbits32/clrbits32/clrsetbits32/setbits64/clrbits64/clrsetbits64 in
 linux/setbits.h

On Fri, Sep 07, 2018 at 03:00:40PM -0500, Scott Wood wrote:
> On Fri, 2018-09-07 at 19:41 +0000, Corentin Labbe wrote:
> > This patch adds setbits32/clrbits32/clrsetbits32 and
> > setbits64/clrbits64/clrsetbits64 in linux/setbits.h header.
> > 
> > Signed-off-by: Corentin Labbe <clabbe@...libre.com>
> > ---
> >  include/linux/setbits.h | 55
> > +++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 55 insertions(+)
> >  create mode 100644 include/linux/setbits.h
> > 
> > diff --git a/include/linux/setbits.h b/include/linux/setbits.h
> > new file mode 100644
> > index 000000000000..3e1e273551bb
> > --- /dev/null
> > +++ b/include/linux/setbits.h
> > @@ -0,0 +1,55 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef __LINUX_SETBITS_H
> > +#define __LINUX_SETBITS_H
> > +
> > +#include <linux/io.h>
> > +
> > +#define __setbits(readfunction, writefunction, addr, set) \
> > +	writefunction((readfunction(addr) | (set)), addr)
> > +#define __clrbits(readfunction, writefunction, addr, mask) \
> > +	writefunction((readfunction(addr) & ~(mask)), addr)
> > +#define __clrsetbits(readfunction, writefunction, addr, mask, set) \
> > +	writefunction(((readfunction(addr) & ~(mask)) | (set)), addr)
> > +#define __setclrbits(readfunction, writefunction, addr, mask, set) \
> > +	writefunction(((readfunction(addr) | (seti)) & ~(mask)), addr)
> > +
> > +#define setbits32(addr, set) __setbits(readl, writel, addr, set)
> > +#define setbits32_relaxed(addr, set) __setbits(readl_relaxed,
> > writel_relaxed, \
> > +					       addr, set)
> > +
> > +#define clrbits32(addr, mask) __clrbits(readl, writel, addr, mask)
> > +#define clrbits32_relaxed(addr, mask) __clrbits(readl_relaxed,
> > writel_relaxed, \
> > +						addr, mask)
> 
> So now setbits32/clrbits32 is implicitly little-endian?  Introducing new
> implicit-endian accessors is probably a bad thing in general, but doing it
> with a name that until this patchset was implicitly big-endian (at least on
> powerpc) seems worse.  Why not setbits32_le()?
> 

I believed that writel/readl was endian agnostic, but It seems that I was wrong.
So I will use _le32.

> 
> > +
> > +#define clrsetbits32(addr, mask, set) __clrsetbits(readl, writel, addr,
> > mask, set)
> > +#define clrsetbits32_relaxed(addr, mask, set) __clrsetbits(readl_relaxed, \
> > +							   writel_relaxed,
> > \
> > +							   addr, mask, set)
> > +
> > +#define setclrbits32(addr, mask, set) __setclrbits(readl, writel, addr,
> > mask, set)
> > +#define setclrbits32_relaxed(addr, mask, set) __setclrbits(readl_relaxed, \
> > +							   writel_relaxed,
> > \
> > +							   addr, mask, set)
> 
> What's the use case for setclrbits?  I don't see it used anywhere in this
> patchset (not even in the coccinelle patterns), it doesn't seem like it would
> be a common pattern, and it could easily get confused with clrsetbits.
> 

It is absent from the coccinelle script due to copy/paste error.
And absent from patchset since it is only two possible example that I can test.

If you run the next fixed coccinelle script, you will find some setclrbits.
Since I fear that mask and set could have some common bits sometimes, I prefer to keep separate clrsetbits and setclrbits.

Regards