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

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Date:   Tue, 7 Jan 2020 14:05:14 +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, 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).

Best regards,
Krzysztof