linux-kernel - Re: [RFC 2/2] clk: per-user clock accounting for debug

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Date:	Sat, 1 Dec 2012 18:30:00 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Rabin Vincent <rabin.vincent@...ricsson.com>
Cc:	Mike Turquette <mturquette@...com>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/2] clk: per-user clock accounting for debug

On Wed, Nov 28, 2012 at 12:52 PM, Rabin Vincent
<rabin.vincent@...ricsson.com> wrote:

> When a clock has multiple users, the WARNING on imbalance of
> enable/disable may not show the guilty party since although they may
> have commited the error earlier, the warning is emitted later when some
> other user, presumably innocent, disables the clock.
>
> Provide per-user clock enable/disable accounting and disabler tracking
> in order to help debug these problems.
>
> NOTE: with this patch, clk_get_parent() behaves like clk_get(), i.e. it
> needs to be matched with a clk_put().  Otherwise, memory will leak.
>
> Signed-off-by: Rabin Vincent <rabin.vincent@...ricsson.com>

Overall this looks very helpful.

> @@ -504,7 +525,15 @@ void clk_disable(struct clk *clk_user)
>         unsigned long flags;
>
>         spin_lock_irqsave(&enable_lock, flags);
> -       __clk_disable(clk);
> +       if (!WARN(clk_user->enable_count == 0,
> +                 "incorrect disable clk dev %s con %s last disabler %pF\n",
> +                 clk_user->dev_id, clk_user->con_id, clk_user->last_disable)) {
> +
> +               clk_user->last_disable = __builtin_return_address(0);
> +               clk_user->enable_count--;
> +
> +               __clk_disable(clk);
> +       }

It seems as if an unbalanced clk_disable() call is done before any
clk_enable() call something like:

"incorrect disable clk dev foo con bar last disabler (null)"

Then the second WARN() will be triggered in __clk_disable().

Have you tried this usecase?

Maybe we can avoid the confusing warning, I don't know.
No big deal maybe.

Apart from that:
Acked-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij
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