linux-kernel - Re: [PATCH] opp: Fix dev_pm_opp_set

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Message-ID: <159718019170.1360974.4800051292737590657@swboyd.mtv.corp.google.com>
Date:   Tue, 11 Aug 2020 14:09:51 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Rajendra Nayak <rnayak@...eaurora.org>, nm@...com,
        viresh.kumar@...aro.org, vireshk@...nel.org
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Rajendra Nayak <rnayak@...eaurora.org>
Subject: Re: [PATCH] opp: Fix dev_pm_opp_set_rate() to not return early

Quoting Rajendra Nayak (2020-08-10 00:06:19)
> dev_pm_opp_set_rate() can now be called with freq = 0 inorder
> to either drop performance or bandwidth votes or to disable
> regulators on platforms which support them.
> In such cases, a subsequent call to dev_pm_opp_set_rate() with
> the same frequency ends up returning early because 'old_freq == freq'
> Instead make it fall through and put back the dropped performance
> and bandwidth votes and/or enable back the regulators.
> 
> Fixes: cd7ea582 ("opp: Make dev_pm_opp_set_rate() handle freq = 0 to drop performance votes")
> Reported-by: Sajida Bhanu <sbhanu@...eaurora.org>
> Signed-off-by: Rajendra Nayak <rnayak@...eaurora.org>
> ---
>  drivers/opp/core.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> index 0c8c74a..a994f30 100644
> --- a/drivers/opp/core.c
> +++ b/drivers/opp/core.c
> @@ -901,6 +901,9 @@ int dev_pm_opp_set_rate(struct device *dev, unsigned long target_freq)
>  
>         /* Return early if nothing to do */
>         if (old_freq == freq) {
> +               if (opp_table->required_opp_tables || opp_table->regulators ||
> +                   opp_table->paths)
> +                       goto skip_clk_only;

This is a goto maze! Any chance we can clean this up?

        if (!opp_table->required_opp_tables && !opp_table->regulators &&
	    !opp_table->paths)
	    if (old_freq == freq) {
		    ret = 0
		    dev_dbg(..)
	    } else if (!_get_opp_count(opp_table)) {
		    ret = _generic_set_opp_clk_only(dev, clk, freq);
	    }
	} else {
		temp_freq = old_freq;
		old_opp = _find_freq_ceil(opp_table, &temp_freq);
		...
	        dev_pm_opp_put(opp);
	put_old_opp:
		if (!IS_ERR(old_opp))
			dev_pm_opp_put(old_opp);
	}
put_opp_table:
	dev_pm_opp_put_opp_table(opp_table);

And that stuff in the else should probably go to another function.

>                 dev_dbg(dev, "%s: old/new frequencies (%lu Hz) are same, nothing to do\n",
>                         __func__, freq);
>                 ret = 0;
> @@ -919,6 +922,7 @@ int dev_pm_opp_set_rate(struct device *dev, unsigned long target_freq)
>                 goto put_opp_table;
>         }
>  
> +skip_clk_only:
>         temp_freq = old_freq;
>         old_opp = _find_freq_ceil(opp_table, &temp_freq);
>         if (IS_ERR(old_opp)) {
> @@ -954,8 +958,10 @@ int dev_pm_opp_set_rate(struct device *dev, unsigned long target_freq)
>                                                  IS_ERR(old_opp) ? NULL : old_opp->supplies,
>                                                  opp->supplies);
>         } else {
> +               ret = 0;
>                 /* Only frequency scaling */
> -               ret = _generic_set_opp_clk_only(dev, clk, freq);
> +               if (freq != old_freq)
> +                       ret = _generic_set_opp_clk_only(dev, clk, freq);
>         }

And write this as 

	else if (freq != old_freq) {
		ret = _generic_set_opp_clk_only(..)
	} else {
		ret = 0;
	}