linux-kernel - Re: [PATCH] drm/panfrost: devfreq: Round frequencies to OPPs

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Date:   Tue, 26 Nov 2019 09:28:14 -0500
From:   Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>
To:     Steven Price <steven.price@....com>
Cc:     Daniel Vetter <daniel@...ll.ch>, David Airlie <airlied@...ux.ie>,
        Rob Herring <robh@...nel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panfrost: devfreq: Round frequencies to OPPs

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>

On Mon, Nov 18, 2019 at 05:30:02PM +0000, Steven Price wrote:
> Currently when setting a frequency in panfrost_devfreq_target the
> returned frequency is the actual frequency that the clock driver reports
> (the return of clk_get_rate()). However, where the provided OPPs don't
> precisely match the frequencies that the clock actually achieves devfreq
> will then complain (repeatedly):
> 
>   devfreq devfreq0: Couldn't update frequency transition information.
> 
> To avoid this change panfrost_devfreq_target() to fetch the opp using
> devfreq_recommened_opp() and not actually query the clock for the
> frequency.
> 
> A similar problem exists with panfrost_devfreq_get_cur_freq(), but in
> this case because the function is optional we can just remove it and
> devfreq will fall back to using the previously set frequency.
> 
> Fixes: 221bc77914cb ("drm/panfrost: Use generic code for devfreq")
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>  drivers/gpu/drm/panfrost/panfrost_devfreq.c | 19 ++++++-------------
>  1 file changed, 6 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.c b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> index 4c4e8a30a1ac..536ba93b0f46 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> @@ -18,15 +18,18 @@ static void panfrost_devfreq_update_utilization(struct panfrost_device *pfdev);
>  static int panfrost_devfreq_target(struct device *dev, unsigned long *freq,
>  				   u32 flags)
>  {
> -	struct panfrost_device *pfdev = dev_get_drvdata(dev);
> +	struct dev_pm_opp *opp;
>  	int err;
>  
> +	opp = devfreq_recommended_opp(dev, freq, flags);
> +	if (IS_ERR(opp))
> +		return PTR_ERR(opp);
> +	dev_pm_opp_put(opp);
> +
>  	err = dev_pm_opp_set_rate(dev, *freq);
>  	if (err)
>  		return err;
>  
> -	*freq = clk_get_rate(pfdev->clock);
> -
>  	return 0;
>  }
>  
> @@ -60,20 +63,10 @@ static int panfrost_devfreq_get_dev_status(struct device *dev,
>  	return 0;
>  }
>  
> -static int panfrost_devfreq_get_cur_freq(struct device *dev, unsigned long *freq)
> -{
> -	struct panfrost_device *pfdev = platform_get_drvdata(to_platform_device(dev));
> -
> -	*freq = clk_get_rate(pfdev->clock);
> -
> -	return 0;
> -}
> -
>  static struct devfreq_dev_profile panfrost_devfreq_profile = {
>  	.polling_ms = 50, /* ~3 frames */
>  	.target = panfrost_devfreq_target,
>  	.get_dev_status = panfrost_devfreq_get_dev_status,
> -	.get_cur_freq = panfrost_devfreq_get_cur_freq,
>  };
>  
>  int panfrost_devfreq_init(struct panfrost_device *pfdev)
> -- 
> 2.20.1
> 

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