linux-kernel - Re: [PATCH v1 4/4] PM / devfreq: tegra30: Check whether clk_round

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Date:   Sun, 19 Sep 2021 18:43:41 +0900
From:   Chanwoo Choi <cwchoi00@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>
Subject: Re: [PATCH v1 4/4] PM / devfreq: tegra30: Check whether
 clk_round_rate() returns zero rate

On 21. 9. 16. 오전 10:28, Dmitry Osipenko wrote:
> 15.09.2021 21:31, Chanwoo Choi пишет:
>> On 21. 9. 15. 오후 12:51, Chanwoo Choi wrote:
>>> Hi,
>>>
>>> On 21. 9. 13. 오전 3:44, Dmitry Osipenko wrote:
>>>> EMC clock is always-on and can't be zero. Check whether clk_round_rate()
>>>> returns zero rate and error out if it does. It can return zero if clock
>>>> tree isn't initialized properly.
>>>>
>>>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>>>> ---
>>>>    drivers/devfreq/tegra30-devfreq.c | 4 ++--
>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/devfreq/tegra30-devfreq.c
>>>> b/drivers/devfreq/tegra30-devfreq.c
>>>> index d83fdc2713ed..65ecf17a36f4 100644
>>>> --- a/drivers/devfreq/tegra30-devfreq.c
>>>> +++ b/drivers/devfreq/tegra30-devfreq.c
>>>> @@ -891,9 +891,9 @@ static int tegra_devfreq_probe(struct
>>>> platform_device *pdev)
>>>>            return err;
>>>>        rate = clk_round_rate(tegra->emc_clock, ULONG_MAX);
>>>> -    if (rate < 0) {
>>>> +    if (rate <= 0) {
>>>>            dev_err(&pdev->dev, "Failed to round clock rate: %ld\n",
>>>> rate);
>>>> -        return rate;
>>>> +        return rate ?: -EINVAL;
>>
>> If rate is 0, It doesn't return and fall-through? even if print the
>> error message. 'return rate ?: -EINVAL;' style is strange for me
>> because it doesn't specify the 'return value' when rate is true.
> 
> It's not clear to me what do you mean by "return and fall-through".
> 
> It specifies the 'return value' when rate is true. It's a short form of
> "rate ? rate : -EINVAL".

I has not known this short form. Thanks for comment. I understand.



-- 
Best Regards,
Samsung Electronics
Chanwoo Choi