linux-kernel - Re: [PATCH v2] clk: let clk_disable() return immediately if clk is NULL or error

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Message-ID: <20160408100600.GI1668@linux-mips.org>
Date:	Fri, 8 Apr 2016 12:06:00 +0200
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	linux-clk@...r.kernel.org,
	Michael Turquette <mturquette@...libre.com>,
	linux-mips@...ux-mips.org, linux-sh@...r.kernel.org,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Eric Miao <eric.y.miao@...il.com>,
	Hartley Sweeten <hsweeten@...ionengravers.com>,
	Greg Ungerer <gerg@...inux.org>,
	Ryan Mallon <rmallon@...il.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Steven Miao <realmz6@...il.com>,
	Simon Horman <horms@...ge.net.au>,
	Wan ZongShun <mcuos.com@...il.com>,
	Rich Felker <dalias@...c.org>,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	adi-buildroot-devel@...ts.sourceforge.net,
	Russell King <linux@....linux.org.uk>,
	linux-m68k@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
	Magnus Damm <magnus.damm@...il.com>,
	John Crispin <blogic@...nwrt.org>,
	Haavard Skinnemoen <hskinnemoen@...il.com>,
	Hans-Christian Egtvedt <egtvedt@...fundet.no>,
	Paul Walmsley <paul@...an.com>,
	Tony Lindgren <tony@...mide.com>, linux-omap@...r.kernel.org,
	Sekhar Nori <nsekhar@...com>, Kevin Hilman <khilman@...nel.org>
Subject: Re: [PATCH v2] clk: let clk_disable() return immediately if clk is
 NULL or error

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@...ionext.com>
> > Acked-by: Greg Ungerer <gerg@...inux.org>
> > Acked-by: Wan Zongshun <mcuos.com@...il.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