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

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Date:   Thu, 16 Sep 2021 04:28:07 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Chanwoo Choi <cwchoi00@...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

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".

The final returned value will be printed by the driver's core. The value
returned by clk_round_rate() is important here since it tells the reason
of the error.

https://elixir.bootlin.com/linux/v5.15-rc1/source/drivers/base/dd.c#L533