linux-kernel - Re: [RESEND PATCH v2 12/16] clk: avoid circular clock topology

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Date:	Mon, 1 Feb 2016 17:08:14 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:	linux-clk@...r.kernel.org,
	Michael Turquette <mturquette@...libre.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v2 12/16] clk: avoid circular clock topology

On 12/28, Masahiro Yamada wrote:
> Currently, clk_register() never checks a circular parent looping,
> but clock providers could register such an insane clock topology.
> For example, "clk_a" could have "clk_b" as a parent, and vice versa.
> In this case, clk_core_reparent() creates a circular parent list
> and __clk_recalc_accuracies() calls itself recursively forever.
> 
> The core infrastructure should be kind enough to bail out, showing
> an appropriate error message in such a case.  This helps to easily
> find a bug in clock providers.  (uh, I made such a silly mistake
> when I was implementing my clock providers first.  I was upset
> because the kernel did not respond, without any error message.)
> 
> This commit adds a new helper function, __clk_is_ancestor().  It
> returns true if the second argument is a possible ancestor of the
> first one.  If a clock core is a possible ancestor of itself, it
> would make a loop when it were registered.  That should be detected
> as an error.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---

Applied to clk-next

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