linux-kernel - Re: [PATCH] sh: clk: Fix discarding const qualifier warning

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Message-ID: <20200107133256.GA648@pi3>
Date:   Tue, 7 Jan 2020 14:32:56 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Linux-sh list <linux-sh@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] sh: clk: Fix discarding const qualifier warning

On Tue, Jan 07, 2020 at 02:05:14PM +0100, Krzysztof Kozlowski wrote:
> On Tue, 7 Jan 2020 at 14:00, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> >
> > Hi Krzysztof,
> >
> > On Tue, Jan 7, 2020 at 1:26 PM Krzysztof Kozlowski <krzk@...nel.org> wrote:
> > > ioreadX() accepts pointer to non-const memory.  This fixes warnings
> > > like:
> > >
> > >     drivers/sh/clk/cpg.c: In function ‘r8’:
> > >     drivers/sh/clk/cpg.c:41:17: warning: passing argument 1 of ‘ioread8’
> > >         discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
> > >
> > > Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
> >
> > Thanks for your patch!
> >
> > > --- a/drivers/sh/clk/cpg.c
> > > +++ b/drivers/sh/clk/cpg.c
> > > @@ -36,17 +36,17 @@ static void sh_clk_write(int value, struct clk *clk)
> > >                 iowrite32(value, clk->mapped_reg);
> > >  }
> > >
> > > -static unsigned int r8(const void __iomem *addr)
> > > +static unsigned int r8(void __iomem *addr)
> > >  {
> > >         return ioread8(addr);
> > >  }
> >
> > Isn't the real issue that some implementations of ioreadX() take const,
> > while others don't?
> >
> > Even the generic ones disagree:
> >
> >     include/asm-generic/io.h:static inline u8 ioread8(const volatile
> > void __iomem *addr)
> >     include/asm-generic/iomap.h:extern unsigned int ioread8(void __iomem *);
> >
> > IMHO they all should take "const volatile void __iomem *".
> 
> Since this is a SuperH driver, I adjusted it to the SuperH
> implementation - lack of const. However iIndeed it makes sense to have
> them all taking "const"... Let me check, if I can fix it (without the
> real HW).

That will be non-trivial because many platforms define ioreadX() with
non-const. For example entire alpha with many its implementations of
ioread(). Even include/asm-generic/iomap.h defines them as non-const...

Best regards,
Krzysztof