linux-kernel - Re: [PATCH v3 2/3] clk: qcom: lpass-sc7180: Disentangle the two clock devices

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Date:   Wed, 14 Oct 2020 15:28:58 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     Taniya Das <tdas@...eaurora.org>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-soc@...r.kernel.org>,
        David Brown <david.brown@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/3] clk: qcom: lpass-sc7180: Disentangle the two clock devices

Hi,

On Wed, Oct 14, 2020 at 3:10 PM Stephen Boyd <sboyd@...nel.org> wrote:
>
> Quoting Douglas Anderson (2020-10-14 14:05:22)
> > diff --git a/drivers/clk/qcom/lpasscorecc-sc7180.c b/drivers/clk/qcom/lpasscorecc-sc7180.c
> > index abcf36006926..48d370e2108e 100644
> > --- a/drivers/clk/qcom/lpasscorecc-sc7180.c
> > +++ b/drivers/clk/qcom/lpasscorecc-sc7180.c
> > @@ -356,12 +356,48 @@ static const struct qcom_cc_desc lpass_audio_hm_sc7180_desc = {
> >         .num_gdscs = ARRAY_SIZE(lpass_audio_hm_sc7180_gdscs),
> >  };
> >
> > +static void lpass_pm_runtime_disable(void *data)
> > +{
> > +       pm_runtime_disable(data);
> > +}
> > +
> > +static void lapss_pm_clk_destroy(void *data)
> > +{
> > +       pm_clk_destroy(data);
> > +}
>
> Why are these helpers added again? And do we even need them? Can't we
> just pass pm_runtime_disable or pm_clk_destroy to the
> devm_add_action_or_reset() second parameter?

Unfortunately, we can't due to the C specification.  Take a look at
all the other users of devm_add_action_or_reset() and they all have
pretty much the same stupid thing.  This is a pretty great grep, for
instance:

git grep devm_add_action_or_reset.*clk_disable_unprepare

I did a quick Google search and the top hit was a stack overflow that
explained it:

https://stackoverflow.com/questions/559581/casting-a-function-pointer-to-another-type

The net-net is that the answer there says:

> Hence, since a void* is not compatible with a struct my_struct*, a
> function pointer of type void (*)(void*) is not compatible with a
> function pointer of type void (*)(struct my_struct*), so this
> casting of function pointers is technically undefined behavior.

I suppose I could try to add devm variants of these functions
somewhere more general if you think it's a good idea, though there it
seems like there's not a huge need since these two greps are zero:

git grep devm_add_action_or_reset.*runtime_disable
git grep devm_add_action_or_reset.*pm_clk_destroy

...actually, do we even need the runtime_disable in the error path?
When the dev goes away does it matter if you left pm_runtime enabled
on it?

-Doug