linux-kernel - Re: [PATCH 2/2] drm/panfrost: Fix incorrect updating of current device frequency

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Message-ID: <f7d05fff-9d23-4706-a93c-a1709872226c@arm.com>
Date:   Mon, 27 Nov 2023 11:34:05 +0000
From:   Steven Price <steven.price@....com>
To:     Adrián Larumbe <adrian.larumbe@...labora.com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Rob Herring <robh@...nel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCH 2/2] drm/panfrost: Fix incorrect updating of current
 device frequency

On 25/11/2023 20:52, Adrián Larumbe wrote:
> It was noticed when setting the Panfrost's DVFS device to the performant
> governor, GPU frequency as reported by fdinfo had dropped to 0 permamently.
> 
> There are two separate issues causing this behaviour:
>  - Not initialising the device's current_frequency variable to its original
>  value during device probe().
>  - Updating said variable in Panfrost devfreq's get_dev_status() rather
>  than after the new OPP's frequency had been retrieved in target(), which
>  meant the old frequency would be assigned instead.

Good catch - I'd not looked at the performance governor. I'd assumed
that one was "too simple to be wrong" ;)

Reviewed-by: Steven Price <steven.price@....com>

> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>
> Fixes: f11b0417eec2 ("drm/panfrost: Add fdinfo support GPU load metrics")
> ---
>  drivers/gpu/drm/panfrost/panfrost_devfreq.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.c b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> index f59c82ea8870..2d30da38c2c3 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> @@ -29,14 +29,20 @@ static void panfrost_devfreq_update_utilization(struct panfrost_devfreq *pfdevfr
>  static int panfrost_devfreq_target(struct device *dev, unsigned long *freq,
>  				   u32 flags)
>  {
> +	struct panfrost_device *ptdev = 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);
>  
> -	return dev_pm_opp_set_rate(dev, *freq);
> +	err =  dev_pm_opp_set_rate(dev, *freq);
> +	if (!err)
> +		ptdev->pfdevfreq.current_frequency = *freq;
> +
> +	return err;
>  }
>  
>  static void panfrost_devfreq_reset(struct panfrost_devfreq *pfdevfreq)
> @@ -58,7 +64,6 @@ static int panfrost_devfreq_get_dev_status(struct device *dev,
>  	spin_lock_irqsave(&pfdevfreq->lock, irqflags);
>  
>  	panfrost_devfreq_update_utilization(pfdevfreq);
> -	pfdevfreq->current_frequency = status->current_frequency;
>  
>  	status->total_time = ktime_to_ns(ktime_add(pfdevfreq->busy_time,
>  						   pfdevfreq->idle_time));
> @@ -164,6 +169,14 @@ int panfrost_devfreq_init(struct panfrost_device *pfdev)
>  
>  	panfrost_devfreq_profile.initial_freq = cur_freq;
>  
> +	/*
> +	 * We could wait until panfrost_devfreq_target() to set this value, but
> +	 * since the simple_ondemand governor works asynchronously, there's a
> +	 * chance by the time someone opens the device's fdinfo file, current
> +	 * frequency hasn't been updated yet, so let's just do an early set.
> +	 */
> +	pfdevfreq->current_frequency = cur_freq;
> +
>  	/*
>  	 * Set the recommend OPP this will enable and configure the regulator
>  	 * if any and will avoid a switch off by regulator_late_cleanup()