linux-kernel - Re: [PATCH v1 4/5] PM / devfreq: tegra30: Use clk_round_rate

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Message-ID: <147b571a-bae1-8a58-942c-579a5297299b@samsung.com>
Date:   Wed, 1 Apr 2020 08:22:45 +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 4/5] PM / devfreq: tegra30: Use
 clk_round_rate_unboundly()

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/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 28b2c7ca416e..34f6291e880c 100644
> --- a/drivers/devfreq/tegra30-devfreq.c
> +++ b/drivers/devfreq/tegra30-devfreq.c
> @@ -834,7 +834,7 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
>  
>  	reset_control_deassert(tegra->reset);
>  
> -	rate = clk_round_rate(tegra->emc_clock, ULONG_MAX);
> +	rate = clk_round_rate_unboundly(tegra->emc_clock, ULONG_MAX);
>  	if (rate < 0) {
>  		dev_err(&pdev->dev, "Failed to round clock rate: %ld\n", rate);
>  		return rate;
> @@ -849,7 +849,7 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
>  	}
>  
>  	for (rate = 0; rate <= tegra->max_freq * KHZ; rate++) {
> -		rate = clk_round_rate(tegra->emc_clock, rate);
> +		rate = clk_round_rate_unboundly(tegra->emc_clock, rate);
>  
>  		if (rate < 0) {
>  			dev_err(&pdev->dev,
> 

Firstly, patch2 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>


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics