Re: [RFC PATCH 08/18] drm/panthor: Skip devfreq when no OPP table is present

[Karunika Choo <karunika.choo@arm.com>]

On 08/06/2026 15:08, Boris Brezillon wrote:
> On Thu, 28 May 2026 16:05:36 +0100
> Karunika Choo <karunika.choo@arm.com> wrote:
> 
>> On Mali v15 AM systems, frequency scaling is handled outside panthor by
>> the AM_GOVERNOR block, so the GPU DT node may not provide an OPP table.
> 
> OOC, is this still handled as clock frequency changes? I'm asking
> because the recent perfcnt work requires registering clk notifiers to
> get an approximation of the number of shader/top-level/coregroup clock
> cycles on a given period of time so we an calculate relative GPU
> utilization, and so far we've only considered clk notifiers as a way to
> get informed of these frequency changes.
> 
> BTW, this is already problematic for the mediatek GPUEB design, where
> devfreq stuff is delegated to an MCU, and we don't currently have a way
> to get notified when this MCU changes the frequencies.
> 

I believe we should still support initializing clocks and registering
notifiers for them. We are just disabling the devfreq subsystem in
this patch.

Would mediatek be able to expose a child clock or logical clock from
ther GPUEB driver to Panthor so that we can get these notifications?

Kind regards,
Karunika Choo

>>
>> Make panthor_devfreq_init() return early when operating-points-v2 is
>> absent, and guard the devfreq helper paths against a missing devfreq
>> instance.
>>
>> This keeps devfreq enabled for existing platforms while allowing v15 AM
>> systems to probe without a local devfreq setup.
>>
>> Signed-off-by: Karunika Choo <karunika.choo@arm.com>
> 
> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
> 
>> ---
>>  drivers/gpu/drm/panthor/panthor_devfreq.c | 13 ++++++++-----
>>  1 file changed, 8 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/panthor/panthor_devfreq.c b/drivers/gpu/drm/panthor/panthor_devfreq.c
>> index 2249b41ca4af..c3252ce54437 100644
>> --- a/drivers/gpu/drm/panthor/panthor_devfreq.c
>> +++ b/drivers/gpu/drm/panthor/panthor_devfreq.c
>> @@ -148,6 +148,9 @@ int panthor_devfreq_init(struct panthor_device *ptdev)
>>  	unsigned long freq = ULONG_MAX;
>>  	int ret;
>>  
>> +	if (!device_property_read_bool(ptdev->base.dev, "operating-points-v2"))
>> +		return 0;
>> +
>>  	pdevfreq = drmm_kzalloc(&ptdev->base, sizeof(*ptdev->devfreq), GFP_KERNEL);
>>  	if (!pdevfreq)
>>  		return -ENOMEM;
>> @@ -267,7 +270,7 @@ void panthor_devfreq_resume(struct panthor_device *ptdev)
>>  {
>>  	struct panthor_devfreq *pdevfreq = ptdev->devfreq;
>>  
>> -	if (!pdevfreq->devfreq)
>> +	if (!pdevfreq || !pdevfreq->devfreq)
>>  		return;
>>  
>>  	panthor_devfreq_reset(pdevfreq);
>> @@ -279,7 +282,7 @@ void panthor_devfreq_suspend(struct panthor_device *ptdev)
>>  {
>>  	struct panthor_devfreq *pdevfreq = ptdev->devfreq;
>>  
>> -	if (!pdevfreq->devfreq)
>> +	if (!pdevfreq || !pdevfreq->devfreq)
>>  		return;
>>  
>>  	drm_WARN_ON(&ptdev->base, devfreq_suspend_device(pdevfreq->devfreq));
>> @@ -290,7 +293,7 @@ void panthor_devfreq_record_busy(struct panthor_device *ptdev)
>>  	struct panthor_devfreq *pdevfreq = ptdev->devfreq;
>>  	unsigned long irqflags;
>>  
>> -	if (!pdevfreq->devfreq)
>> +	if (!pdevfreq || !pdevfreq->devfreq)
>>  		return;
>>  
>>  	spin_lock_irqsave(&pdevfreq->lock, irqflags);
>> @@ -306,7 +309,7 @@ void panthor_devfreq_record_idle(struct panthor_device *ptdev)
>>  	struct panthor_devfreq *pdevfreq = ptdev->devfreq;
>>  	unsigned long irqflags;
>>  
>> -	if (!pdevfreq->devfreq)
>> +	if (!pdevfreq || !pdevfreq->devfreq)
>>  		return;
>>  
>>  	spin_lock_irqsave(&pdevfreq->lock, irqflags);
>> @@ -323,7 +326,7 @@ unsigned long panthor_devfreq_get_freq(struct panthor_device *ptdev)
>>  	unsigned long freq = 0;
>>  	int ret;
>>  
>> -	if (!pdevfreq->devfreq)
>> +	if (!pdevfreq || !pdevfreq->devfreq)
>>  		return 0;
>>  
>>  	ret = pdevfreq->devfreq->profile->get_cur_freq(ptdev->base.dev, &freq);
>