Date: Mon, 2 Feb 2015 22:31:29 +0100 (CET)
From: Julia Lawall <julia.lawall@lip6.fr>
To: Stephen Boyd <sboyd@codeaurora.org>
cc: Julia Lawall <Julia.Lawall@lip6.fr>,
        Mike Turquette <mturquette@linaro.org>,
        Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        linux-kernel@vger.kernel.org, Paul Walmsley <paul@pwsan.com>,
        Tony Lindgren <tony@atomide.com>, linux-omap@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, t-kristo@ti.com,
        cocci@systeme.lip6.fr
Subject: Re: [PATCH v13 3/6] clk: Make clk API return per-user struct clk
 instances
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References: <1422011024-32283-1-git-send-email-tomeu.vizoso@collabora.com> <1422011024-32283-4-git-send-email-tomeu.vizoso@collabora.com> <20150201212432.22722.70917@quantum> <54CFE1FE.7040404@codeaurora.org>
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On Mon, 2 Feb 2015, Stephen Boyd wrote:

> On 02/01/15 13:24, Mike Turquette wrote:
> > Quoting Tomeu Vizoso (2015-01-23 03:03:30)
> >> Moves clock state to struct clk_core, but takes care to change as little API as
> >> possible.
> >>
> >> struct clk_hw still has a pointer to a struct clk, which is the
> >> implementation's per-user clk instance, for backwards compatibility.
> >>
> >> The struct clk that clk_get_parent() returns isn't owned by the caller, but by
> >> the clock implementation, so the former shouldn't call clk_put() on it.
> >>
> >> Because some boards in mach-omap2 still register clocks statically, their clock
> >> registration had to be updated to take into account that the clock information
> >> is stored in struct clk_core now.
> > Tero, Paul & Tony,
> >
> > Tomeu's patch unveils a problem with omap3_noncore_dpll_enable and
> > struct dpll_data, namely this snippet from
> > arch/arm/mach-omap2/dpll3xxx.c:
> >
> >         parent = __clk_get_parent(hw->clk);
> >
> >         if (__clk_get_rate(hw->clk) == __clk_get_rate(dd->clk_bypass)) {
> >                 WARN(parent != dd->clk_bypass,
> >                                 "here0, parent name is %s, bypass name is %s\n",
> >                                 __clk_get_name(parent), __clk_get_name(dd->clk_bypass));
> >                 r = _omap3_noncore_dpll_bypass(clk);
> >         } else {
> >                 WARN(parent != dd->clk_ref,
> >                                 "here1, parent name is %s, ref name is %s\n",
> >                                 __clk_get_name(parent), __clk_get_name(dd->clk_ref));
> >                 r = _omap3_noncore_dpll_lock(clk);
> >         }
> >
> > struct dpll_data has members clk_ref and clk_bypass which are struct clk
> > pointers. This was always a bit of a violation of the clk.h contract
> > since drivers are not supposed to deref struct clk pointers. 
> 
> Julia,
> 
> Is there a way we can write a coccinelle script to check for this? The
> goal being to find all drivers that are comparing struct clk pointers or
> attempting to dereference them. There are probably other frameworks that
> could use the same type of check (regulator, gpiod, reset, pwm, etc.).
> Probably anything that has a get/put API.

Comparing or dereferencing pointers of a particular type should be 
straightforward to check for.  Is there an example of how to use the 
parent_index value to fix the problem?

julia


> 
> -Stephen
> 
> > Now that we
> > generate unique pointers for each call to clk_get (clk_ref & clk_bypass
> > are populated by of_clk_get in ti_clk_register_dpll) then the pointer
> > comparisons above will never be equal (even if they resolve down to the
> > same struct clk_core). I added the verbose traces to the WARNs above to
> > illustrate the point: the names are always the same but the pointers
> > differ.
> >
> > AFAICT this doesn't break anything, but booting on OMAP3+ results in
> > noisy WARNs.
> >
> > I think the correct fix is to replace clk_bypass and clk_ref pointers
> > with a simple integer parent_index. In fact we already have this index.
> > See how the pointers are populated in ti_clk_register_dpll:
> >
> >
> >         dd->clk_ref = of_clk_get(node, 0);
> >         dd->clk_bypass = of_clk_get(node, 1);
> >
> > Tony, the same problem affects the FAPLL code which copy/pastes some of
> > the DPLL code.
> >
> > Thoughts?
> >
> -- 
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> a Linux Foundation Collaborative Project
> 
> 
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