linux-kernel - Re: [PATCH V2 1/3] clk: add clk_bulk

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Date:   Tue, 9 May 2017 20:14:35 +0800
From:   Dong Aisheng <dongas86@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Dong Aisheng <aisheng.dong@....com>,
        linux-clk <linux-clk@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Mark Brown <broonie@...nel.org>,
        Robin Gong <yibin.gong@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Fabio Estevam <fabio.estevam@....com>, anson.huang@....com,
        Bai Ping <ping.bai@....com>,
        Leonard Crestez <leonard.crestez@....com>,
        Octavian Purdila <octavian.purdila@....com>,
        Russell King <linux@...linux.org.uk>,
        Florian Fainelli <f.fainelli@...il.com>,
        Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH V2 1/3] clk: add clk_bulk_get accessories

Hi Geert,

On Mon, May 8, 2017 at 11:08 PM, Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> Hi Dong,
>
> On Mon, May 8, 2017 at 4:03 PM, Dong Aisheng <aisheng.dong@....com> wrote:
>> --- /dev/null
>> +++ b/drivers/clk/clk-bulk.c
>> @@ -0,0 +1,165 @@
>
>> +int __must_check clk_bulk_get(struct device *dev, int num_clks,
>> +                             struct clk_bulk_data *clks)
>> +{
>> +       int ret;
>> +       int i;
>> +
>> +       for (i = 0; i < num_clks; i++)
>> +               clks[i].clk = NULL;
>> +
>> +       for (i = 0; i < num_clks; i++) {
>> +               clks[i].clk = clk_get(dev, clks[i].id);
>> +               if (IS_ERR(clks[i].clk)) {
>> +                       ret = PTR_ERR(clks[i].clk);
>> +                       dev_err(dev, "Failed to get clk '%s': %d\n",
>> +                               clks[i].id, ret);
>> +                       clks[i].clk = NULL;
>> +                       goto err;
>> +               }
>> +       }
>> +
>> +       return 0;
>> +
>> +err:
>> +       while (--i >= 0)
>> +               clk_put(clks[i].clk);
>
> These are released in inverse order, which is good.
>
>> +
>> +       return ret;
>> +}
>> +EXPORT_SYMBOL(clk_bulk_get);
>> +
>> +void clk_bulk_put(int num_clks, struct clk_bulk_data *clks)
>> +{
>> +       int i;
>> +
>> +       for (i = 0; i < num_clks; i++) {
>> +               clk_put(clks[i].clk);
>> +               clks[i].clk = NULL;
>
> These aren't.
>
> Typically resources are released in the inverse order. Not doing so may
> cause subtle issues.
>
> I can't come up with an example. but I'm quite sure the real world will find
> one soon ;-)
>
> The same is true for enable vs. disable, and prepare vs. unprepare.
>

I thought of it before and was wondering whether it's necessary to do it
as i believe it may be wrong for drivers to reply on the clk_bulk API to
do some some magic ordering to make things run because the API does not
guarantee it.

But i do agree with you that it might be a common sense to release resource
in inverse order, just harmless to do it!
So i will make it in V3 if no objection from Maintainer later.

Thanks for your suggestion!

Regards
Dong Aisheng

> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
> --
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