linux-kernel - Re: [PATCH v1 3/5] PM / devfreq: tegra20: Use clk_round_rate

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Message-ID: <d74555b7-81c5-0c00-9c4e-3d923e8e6e5d@samsung.com>
Date:   Wed, 1 Apr 2020 08:23:30 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     linux-clk@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/5] PM / devfreq: tegra20: Use
 clk_round_rate_unboundly()

On 4/1/20 8:22 AM, Chanwoo Choi wrote:
> Hi Dmitry,
> 
> On 3/31/20 8:16 AM, Dmitry Osipenko wrote:
>> The clk_round_rate() doesn't work for us properly if clock rate is bounded
>> by a min/max rate that is requested by some other clk-user because we're
>> building devfreq's OPP table based on the rounding.
>>
>> In particular this becomes a problem if display driver is probed earlier
>> than devfreq, and thus, display adds a memory bandwidth request using
>> interconnect API, which results in a minimum clock-rate being set for
>> the memory clk. In a result, the lowest devfreq OPP rate is getting
>> limited to the minimum rate imposed by the display driver.
>>
>> Let's use new clk_round_rate_unboundly() that resolves the problem by
>> rounding clock rate without taking into account min/max limits imposed by
>> active clk users.
>>
>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>> ---
>>  drivers/devfreq/tegra20-devfreq.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/devfreq/tegra20-devfreq.c b/drivers/devfreq/tegra20-devfreq.c
>> index ff82bac9ee4e..1bb10ef11dfe 100644
>> --- a/drivers/devfreq/tegra20-devfreq.c
>> +++ b/drivers/devfreq/tegra20-devfreq.c
>> @@ -149,10 +149,10 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
>>  
>>  	tegra->regs = mc->regs;
>>  
>> -	max_rate = clk_round_rate(tegra->emc_clock, ULONG_MAX);
>> +	max_rate = clk_round_rate_unboundly(tegra->emc_clock, ULONG_MAX);
>>  
>>  	for (rate = 0; rate <= max_rate; rate++) {
>> -		rate = clk_round_rate(tegra->emc_clock, rate);
>> +		rate = clk_round_rate_unboundly(tegra->emc_clock, rate);
>>  
>>  		err = dev_pm_opp_add(&pdev->dev, rate, 0);
>>  		if (err) {
>>
> 
> Firstly, patch1 have to be reviewed for this patch.
> I have no any objection. It looks good to me.
> 
> If patch1 get the confirmation from clock maintainer,
> feel free to add my acked tag:
> Acked-by: Chanwoo Choi <cw00.choi@...sung.com>
> 

Sorry. I mean the patch2 about clk_round_rate_unboundly() function.
instead of patch1. 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics