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

[Boris Brezillon <boris.brezillon@collabora.com>]

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.

> 
> 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);