linux-kernel - Re: [PATCH v2 03/19] PM / devfreq: tegra: Don't ignore clk errors

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Message-ID: <485c7af3-453a-1c89-a677-3ef622ee2ad3@gmail.com>
Date:   Tue, 16 Apr 2019 16:42:47 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Chanwoo Choi <cw00.choi@...sung.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:     linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 03/19] PM / devfreq: tegra: Don't ignore clk errors

16.04.2019 4:52, Chanwoo Choi пишет:
> Hi,
> 
> On 19. 4. 15. 오후 11:54, Dmitry Osipenko wrote:
>> The clk_set_min_rate() could fail and in this case clk_set_rate() sets
>> rate to 0, which may drop EMC rate to minimum and make machine very
>> difficult to use.
>>
>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>> ---
>>  drivers/devfreq/tegra-devfreq.c | 10 ++++++++--
>>  1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/devfreq/tegra-devfreq.c b/drivers/devfreq/tegra-devfreq.c
>> index 0c0909fba545..69581c9082d4 100644
>> --- a/drivers/devfreq/tegra-devfreq.c
>> +++ b/drivers/devfreq/tegra-devfreq.c
>> @@ -487,6 +487,7 @@ static int tegra_devfreq_target(struct device *dev, unsigned long *freq,
>>  	struct tegra_devfreq *tegra = dev_get_drvdata(dev);
>>  	struct dev_pm_opp *opp;
>>  	unsigned long rate;
>> +	int err;
>>  
>>  	opp = devfreq_recommended_opp(dev, freq, flags);
>>  	if (IS_ERR(opp)) {
>> @@ -496,8 +497,13 @@ static int tegra_devfreq_target(struct device *dev, unsigned long *freq,
>>  	rate = dev_pm_opp_get_freq(opp);
>>  	dev_pm_opp_put(opp);
>>  
>> -	clk_set_min_rate(tegra->emc_clock, rate);
>> -	clk_set_rate(tegra->emc_clock, 0);
>> +	err = clk_set_min_rate(tegra->emc_clock, rate);
>> +	if (err)
>> +		return err;
>> +
>> +	err = clk_set_rate(tegra->emc_clock, 0);
>> +	if (err)
> 
> Why don't you restore the previous minimum clock for tegra->emc_clock
> when failed to execute 'clk_set_rate(tegra->emc_clock, 0);'?
> 
> I think that if you control the restoring the previous minimum clock,
> it is more nice to handle the error handling.

I now see that devfreq has the previous_freq field and indeed it is possible to restore the min_rate value using it. Thanks for the suggestion.