linux-kernel - Re: [PATCH] drm/panfrost: Add missing OPP table refcnt decremental

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Message-ID: <4c8cf37c-1576-4633-9f75-01e26e95f6c2@arm.com>
Date: Thu, 3 Oct 2024 11:29:55 +0100
From: Steven Price <steven.price@....com>
To: Boris Brezillon <boris.brezillon@...labora.com>,
 Adrián Larumbe <adrian.larumbe@...labora.com>
Cc: 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>, Simona Vetter <simona@...ll.ch>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 kernel@...labora.com, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panfrost: Add missing OPP table refcnt decremental

On 03/10/2024 08:17, Boris Brezillon wrote:
> On Thu,  3 Oct 2024 01:25:37 +0100
> Adrián Larumbe <adrian.larumbe@...labora.com> wrote:
> 
>> Commit f11b0417eec2 ("drm/panfrost: Add fdinfo support GPU load metrics")
>> retrieves the OPP for the maximum device clock frequency, but forgets to
>> keep the reference count balanced by putting the returned OPP object. This
>> eventually leads to an OPP core warning when removing the device.
>>
>> Fix it by putting OPP objects as many times as they're retrieved.
>> Also remove an unnecessary whitespace.
>>
>> Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>
>> Fixes: f11b0417eec2 ("drm/panfrost: Add fdinfo support GPU load metrics")
> 
> Reviewed-by: 

I assume that tag shouldn't be there ;)

>> ---
>>  drivers/gpu/drm/panfrost/panfrost_devfreq.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.c b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
>> index 2d30da38c2c3..c7d3f980f1e5 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_devfreq.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
>> @@ -38,7 +38,7 @@ static int panfrost_devfreq_target(struct device *dev, unsigned long *freq,
>>  		return PTR_ERR(opp);
>>  	dev_pm_opp_put(opp);
>>  
>> -	err =  dev_pm_opp_set_rate(dev, *freq);
>> +	err = dev_pm_opp_set_rate(dev, *freq);
>>  	if (!err)
>>  		ptdev->pfdevfreq.current_frequency = *freq;
>>  
>> @@ -177,6 +177,8 @@ int panfrost_devfreq_init(struct panfrost_device *pfdev)
>>  	 */
>>  	pfdevfreq->current_frequency = cur_freq;
>>  
>> +	dev_pm_opp_put(opp);
>> +
> 
> Shouldn't this be moved after the dev_pm_opp_set_opp() that's
> following?

I agree.

I'm not sure what the devfreq maintainers would think, but there's now a
few drivers that basically want find_available_max_freq() exported - if
you're interested in a wider cleanup then it might be worth looking at.

Steve

>>  	/*
>>  	 * Set the recommend OPP this will enable and configure the regulator
>>  	 * if any and will avoid a switch off by regulator_late_cleanup()
>