linux-kernel - Re: [PATCH v2 1/4] clk: add common __clk_get(), __clk

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Message-ID: <20130820203034.GC17845@n2100.arm.linux.org.uk>
Date:	Tue, 20 Aug 2013 21:30:34 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Sylwester Nawrocki <s.nawrocki@...sung.com>
Cc:	linux-arm-kernel@...ts.infradead.org, mturquette@...aro.org,
	jiada_wang@...tor.com, robherring2@...il.com,
	grant.likely@...aro.org, broonie@...nel.org, vapier@...too.org,
	ralf@...ux-mips.org, kyungmin.park@...sung.com,
	shawn.guo@...aro.org, sebastian.hesselbarth@...il.com,
	LW@...O-electronics.de, t.figa@...sung.com, g.liakhovetski@....de,
	laurent.pinchart@...asonboard.com, linux-kernel@...r.kernel.org,
	uclinux-dist-devel@...ckfin.uclinux.org, linux-mips@...ux-mips.org,
	linux-sh@...r.kernel.org
Subject: Re: [PATCH v2 1/4] clk: add common __clk_get(), __clk_put()
	implementations

On Tue, Aug 20, 2013 at 07:34:20PM +0200, Sylwester Nawrocki wrote:
> +int __clk_get(struct clk *clk)
> +{
> +	if (WARN_ON((!clk)))
> +		return 0;

This changes the behaviour of clk_get()

> +
> +	if (!try_module_get(clk->owner))
> +		return 0;

If you want this to be safe against NULL pointers, just do this:

	if (clk && !try_module_get(clk->owner))
		return 0;

> +
> +	return 1;
> +}
> +EXPORT_SYMBOL(__clk_get);
> +
> +void __clk_put(struct clk *clk)
> +{
> +	if (!clk || IS_ERR(clk))
> +		return;
> +
> +	module_put(clk->owner);

Calling clk_put() with an error-pointer should be a Bad Thing and something
that shouldn't be encouraged, so trapping it is probably unwise.  So, just
do here:

	if (clk)
		module_put(clk->owner);

If we do have some callers of this with ERR pointers, then we could add:

	if (WARN_ON_ONCE(IS_ERR(clk)))
		return;

and remove it after a full kernel cycle or so.
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