linux-kernel - Re: [PATCH 02/10] PM / devfreq: Do not require devices to have OPPs

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Message-ID: <114afa7e-6218-6b1f-f87e-84690f10029c@samsung.com>
Date:   Thu, 30 Sep 2021 13:19:29 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Samuel Holland <samuel@...lland.org>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/10] PM / devfreq: Do not require devices to have OPPs

Hi Samuel,


On 9/29/21 1:42 PM, Samuel Holland wrote:
> Since commit ea572f816032 ("PM / devfreq: Change return type of
> devfreq_set_freq_table()"), all devfreq devices are required to have a
> valid freq_table. If freq_table is not provided by the driver, it will
> be filled in by set_freq_table() from the OPPs; if that fails,
> devfreq_add_device() will return an error.
> 
> However, since commit ab8f58ad72c4 ("PM / devfreq: Set min/max_freq when
> adding the devfreq device"), devfreq devices are _also_ required to have
> an OPP table, even if they provide freq_table. devfreq_add_device()
> requires dev_pm_opp_find_freq_ceil() and dev_pm_opp_find_freq_floor() to
> return successfully, specifically to initialize scaling_min/max_freq.
> 
> Not all drivers need an OPP table. For example, a driver where all
> frequencies are determined dynamically could work by filling out only
> freq_table. But with the current code it must call dev_pm_opp_add() on
> every freq_table entry to probe successfully.

As you commented, if device has no opp table, it should call dev_pm_opp_add().
The devfreq have to use OPP for controlling the frequency/regulator.

Actually, I want that all devfreq driver uses the OPP as default way.
Are there any reason why don't use the OPP table?

> 
> The offending properties, scaling_min/max_freq, are only necessary if a
> device has OPPs; if no OPPs exist at all, OPPs cannot be dynamically
> enabled or disabled, so those values have no effect. Thus it is trivial
> to restore support for devices with freq_table only and not OPPs -- move
> those initializations behind the check for a valid OPP table.
> 
> Since get_freq_range() uses scaling_max_freq in a min() expression, it
> must be initialized to the maximum possible value. scaling_min_freq is
> initialized as well for consistency.
> 
> Fixes: ab8f58ad72c4 ("PM / devfreq: Set min/max_freq when adding the devfreq device")
> Signed-off-by: Samuel Holland <samuel@...lland.org>
> ---
>  drivers/devfreq/devfreq.c | 36 ++++++++++++++++++++----------------
>  1 file changed, 20 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 7a8b022ba456..426e31e6c448 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -835,24 +835,28 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  		mutex_lock(&devfreq->lock);
>  	}
>  
> -	devfreq->scaling_min_freq = find_available_min_freq(devfreq);
> -	if (!devfreq->scaling_min_freq) {
> -		mutex_unlock(&devfreq->lock);
> -		err = -EINVAL;
> -		goto err_dev;
> -	}
> -
> -	devfreq->scaling_max_freq = find_available_max_freq(devfreq);
> -	if (!devfreq->scaling_max_freq) {
> -		mutex_unlock(&devfreq->lock);
> -		err = -EINVAL;
> -		goto err_dev;
> -	}
> -
> -	devfreq->suspend_freq = dev_pm_opp_get_suspend_opp_freq(dev);
>  	devfreq->opp_table = dev_pm_opp_get_opp_table(dev);
> -	if (IS_ERR(devfreq->opp_table))
> +	if (IS_ERR(devfreq->opp_table)) {
>  		devfreq->opp_table = NULL;
> +		devfreq->scaling_min_freq = 0;
> +		devfreq->scaling_max_freq = ULONG_MAX;
> +	} else {
> +		devfreq->scaling_min_freq = find_available_min_freq(devfreq);
> +		if (!devfreq->scaling_min_freq) {
> +			mutex_unlock(&devfreq->lock);
> +			err = -EINVAL;
> +			goto err_dev;
> +		}
> +
> +		devfreq->scaling_max_freq = find_available_max_freq(devfreq);
> +		if (!devfreq->scaling_max_freq) {
> +			mutex_unlock(&devfreq->lock);
> +			err = -EINVAL;
> +			goto err_dev;
> +		}
> +
> +		devfreq->suspend_freq = dev_pm_opp_get_suspend_opp_freq(dev);
> +	}
>  
>  	atomic_set(&devfreq->suspend_count, 0);
>  
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics