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Date: Fri, 8 Apr 2016 20:15:05 +0900
Message-ID: <CAK7LNASmvJfmFKVLWpQ8GZYKs6ntSk1Lae-witX=1hDGotQV_Q@mail.gmail.com>
Subject: Re: [PATCH v2] clk: let clk_disable() return immediately if clk is
 NULL or error
From: Masahiro Yamada <yamada.masahiro@socionext.com>
To: Ralf Baechle <ralf@linux-mips.org>, Stephen Boyd <sboyd@codeaurora.org>
Cc: linux-mips@linux-mips.org, linux-m68k@vger.kernel.org,
        Rich Felker <dalias@libc.org>, linux-sh@vger.kernel.org,
        Tony Lindgren <tony@atomide.com>,
        Michael Turquette <mturquette@baylibre.com>,
        Sekhar Nori <nsekhar@ti.com>, Greg Ungerer <gerg@uclinux.org>,
        linux-clk@vger.kernel.org,
        Hans-Christian Egtvedt <egtvedt@samfundet.no>,
        Russell King <linux@arm.linux.org.uk>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Kevin Hilman <khilman@kernel.org>, Magnus Damm <magnus.damm@gmail.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Haavard Skinnemoen <hskinnemoen@gmail.com>,
        Wan ZongShun <mcuos.com@gmail.com>, Steven Miao <realmz6@gmail.com>,
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        Hartley Sweeten <hsweeten@visionengravers.com>
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2016-04-08 19:06 GMT+09:00 Ralf Baechle <ralf@linux-mips.org>:
> On Thu, Apr 07, 2016 at 05:33:28PM -0700, Stephen Boyd wrote:
>
>> On 04/05, Masahiro Yamada wrote:
>> > The clk_disable() in the common clock framework (drivers/clk/clk.c)
>> > returns immediately if a given clk is NULL or an error pointer.  It
>> > allows clock consumers to call clk_disable() without IS_ERR_OR_NULL
>> > checking if drivers are only used with the common clock framework.
>> >
>> > Unfortunately, NULL/error checking is missing from some of non-common
>> > clk_disable() implementations.  This prevents us from completely
>> > dropping NULL/error checking from callers.  Let's make it tree-wide
>> > consistent by adding IS_ERR_OR_NULL(clk) to all callees.
>> >
>> > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
>> > Acked-by: Greg Ungerer <gerg@uclinux.org>
>> > Acked-by: Wan Zongshun <mcuos.com@gmail.com>
>> > ---
>> >
>> > Stephen,
>> >
>> > This patch has been unapplied for a long time.
>> >
>> > Please let me know if there is something wrong with this patch.
>> >
>>
>> I'm mostly confused why we wouldn't want to encourage people to
>> call clk_disable or unprepare on a clk that's an error pointer.
>> Typically an error pointer should be dealt with, instead of
>> silently ignored, so why wasn't it dealt with by passing it up
>> the probe() path?
>
> While your argument makes perfect sense, Many clk_disable implementations
> are already doing similar checks, for example:
>
> arch/arm/mach-davinci/clock.c:
>
> void clk_disable(struct clk *clk)
> {
>         unsigned long flags;
>
>         if (clk == NULL || IS_ERR(clk))
>                 return;
> [...]
>
> arch/arm/mach-omap1/clock.c
>
> void clk_disable(struct clk *clk)
> {
>         unsigned long flags;
>
>         if (clk == NULL || IS_ERR(clk))
>                 return;
> [...]
>
> arch/avr32/mach-at32ap/clock.c
>
> void clk_disable(struct clk *clk)
> {
>         unsigned long flags;
>
>         if (IS_ERR_OR_NULL(clk))
>                 return;
> [...]
>
> arch/mips/lantiq/clk.c:
>
> static inline int clk_good(struct clk *clk)
> {
>         return clk && !IS_ERR(clk);
> }
>
> [...]
>
> void clk_disable(struct clk *clk)
> {
>         if (unlikely(!clk_good(clk)))
>                 return;
>
>         if (clk->disable)
> [...]
>
> So should we go and weed out these checks?
>
>   Ralf


Please help me understand your thought clearly.

[1] Should calling clk_unprepare/disable() with a NULL pointer be allowed?

[2] Should calling clk_unprepare/disable() with an error pointer be allowed?


-- 
Best Regards
Masahiro Yamada