linux-kernel - Re: [PATCH 07/13] opp: Allow _generic_set_opp_clk

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Date:   Tue, 26 Jan 2021 00:09:06 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Sibi Sankar <sibis@...eaurora.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 07/13] opp: Allow _generic_set_opp_clk_only() to work for
 non-freq devices

22.01.2021 07:35, Viresh Kumar пишет:
> On 21-01-21, 23:26, Dmitry Osipenko wrote:
>> 21.01.2021 14:17, Viresh Kumar пишет:
>>> In order to avoid conditional statements at the caller site, this patch
>>> updates _generic_set_opp_clk_only() to work for devices that don't
>>> change frequency (like power domains, etc.). Return 0 if the clk pointer
>>> passed to this routine is not valid.
>>>
>>> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
>>> ---
>> ...
>>
>> Hello Viresh,
>>
>> Thank you very much for yours effort! I gave a quick test to this series
>> and instantly found one small issue in this patch.
>>
>>> +	/* We may reach here for devices which don't change frequency */
>>> +	if (unlikely(!clk))
>>
>> I replaced dev_pm_opp_set_voltage() with dev_pm_opp_set_opp() in the
>> Tegra PD driver and got a crash, which happens because the above line
>> should be:
>>
>> 	if (IS_ERR(clk))
> 
> Fixed, thanks.
> 

Please remove unlikely() around IS_ERR(), it already has the unlikely().

https://elixir.bootlin.com/linux/v5.11-rc4/source/include/linux/err.h#L22

I'd also recommend to remove all the unlikely() from OPP code since it
doesn't bring any value if not used in a very performance-critical code
path. OPP core doesn't have such code paths. The [un]likely() only make
code less readable and may result in a worse assembly.