Re: [PATCH 1/2] drm/panthor: Add tracepoint for hardware utilisation changes

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

On 03/12/2025 13:56, Nicolas Frattaroli wrote:
> Mali GPUs have three registers that indicate which parts of the hardware
> are powered and active at any moment. These take the form of bitmaps. In
> the case of SHADER_PWRACTIVE for example, a high bit indicates that the
> shader core corresponding to that bit index is active. These bitmaps
> aren't solely contiguous bits, as it's common to have holes in the
> sequence of shader core indices, and the actual set of which cores are
> present is defined by the "shader present" register.
> 
> When the GPU finishes a power state transition, it fires a
> GPU_IRQ_POWER_CHANGED_ALL interrupt. After such an interrupt is
> received, the PWRACTIVE registers will likely contain interesting new
> information.
> 
> This is not to be confused with the PWR_IRQ_POWER_CHANGED_ALL interrupt,
> which is something related to Mali v14+'s power control logic. The
> PWRACTIVE registers and corresponding interrupts are already available
> in v9 and onwards.
> 
> Expose this as a tracepoint to userspace. This allows users to debug
> various scenarios and gather interesting information, such as: knowing
> how much hardware is lit up at any given time, correlating graphics
> corruption with a specific active shader core, measuring when hardware
> is allowed to go to an inactive state again, and so on.
> 
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_device.c |  1 +
>  drivers/gpu/drm/panthor/panthor_gpu.c    |  9 ++++++++
>  drivers/gpu/drm/panthor/panthor_trace.h  | 38 ++++++++++++++++++++++++++++++++
>  3 files changed, 48 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
> index e133b1e0ad6d..a3cb934104b8 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.c
> +++ b/drivers/gpu/drm/panthor/panthor_device.c
> @@ -548,6 +548,7 @@ int panthor_device_resume(struct device *dev)
>  			    DRM_PANTHOR_USER_MMIO_OFFSET, 0, 1);
>  	atomic_set(&ptdev->pm.state, PANTHOR_DEVICE_PM_STATE_ACTIVE);
>  	mutex_unlock(&ptdev->pm.mmio_lock);
> +
>  	return 0;
>  
>  err_suspend_devfreq:
> diff --git a/drivers/gpu/drm/panthor/panthor_gpu.c b/drivers/gpu/drm/panthor/panthor_gpu.c
> index 9cb5dee93212..8830aa9a5c4b 100644
> --- a/drivers/gpu/drm/panthor/panthor_gpu.c
> +++ b/drivers/gpu/drm/panthor/panthor_gpu.c
> @@ -22,6 +22,9 @@
>  #include "panthor_hw.h"
>  #include "panthor_regs.h"
>  
> +#define CREATE_TRACE_POINTS
> +#include "panthor_trace.h"
> +
>  /**
>   * struct panthor_gpu - GPU block management data.
>   */
> @@ -46,6 +49,7 @@ struct panthor_gpu {
>  	(GPU_IRQ_FAULT | \
>  	 GPU_IRQ_PROTM_FAULT | \
>  	 GPU_IRQ_RESET_COMPLETED | \
> +	 GPU_IRQ_POWER_CHANGED_ALL | \
>  	 GPU_IRQ_CLEAN_CACHES_COMPLETED)
>  
>  static void panthor_gpu_coherency_set(struct panthor_device *ptdev)
> @@ -97,6 +101,11 @@ static void panthor_gpu_irq_handler(struct panthor_device *ptdev, u32 status)
>  		wake_up_all(&ptdev->gpu->reqs_acked);
>  	}
>  	spin_unlock(&ptdev->gpu->reqs_lock);
> +
> +	if (status & GPU_IRQ_POWER_CHANGED_ALL)
> +		trace_gpu_power_active(gpu_read64(ptdev, SHADER_PWRACTIVE),
> +				       gpu_read64(ptdev, TILER_PWRACTIVE),
> +				       gpu_read64(ptdev, L2_PWRACTIVE));
>  }
>  PANTHOR_IRQ_HANDLER(gpu, GPU, panthor_gpu_irq_handler);
>  
> diff --git a/drivers/gpu/drm/panthor/panthor_trace.h b/drivers/gpu/drm/panthor/panthor_trace.h
> new file mode 100644
> index 000000000000..01013f81e68a
> --- /dev/null
> +++ b/drivers/gpu/drm/panthor/panthor_trace.h
> @@ -0,0 +1,38 @@
> +/* SPDX-License-Identifier: GPL-2.0 or MIT */
> +/* Copyright 2025 Collabora ltd. */
> +
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM panthor
> +
> +#if !defined(__PANTHOR_TRACE_H__) || defined(TRACE_HEADER_MULTI_READ)
> +#define __PANTHOR_TRACE_H__
> +
> +#include <linux/tracepoint.h>
> +#include <linux/types.h>
> +
> +TRACE_EVENT(gpu_power_active,
> +	TP_PROTO(u64 shader_bitmap, u64 tiler_bitmap, u64 l2_bitmap),

nit: if you want to add tracing can we also add the device name as
well? Something like:

  TP_PROTO(struct device *dev, ...),
  TP_ARGS(dev, ...),
  TP_STRUCT__ENTRY(
          __string(dev_name, dev_name(dev))
          ...
  ).
  ...

This will help differentiate the device it is originating from in
a multi GPU situation.

Kind regards,
Karunika

> +	TP_ARGS(shader_bitmap, tiler_bitmap, l2_bitmap),
> +	TP_STRUCT__entry(
> +		__field(u64, shader_bitmap)
> +		__field(u64, tiler_bitmap)
> +		__field(u64, l2_bitmap)
> +	),
> +	TP_fast_assign(
> +		__entry->shader_bitmap	= shader_bitmap;
> +		__entry->tiler_bitmap	= tiler_bitmap;
> +		__entry->l2_bitmap	= l2_bitmap;
> +	),
> +	TP_printk("shader_bitmap=0x%llx tiler_bitmap=0x%llx l2_bitmap=0x%llx",
> +		  __entry->shader_bitmap, __entry->tiler_bitmap, __entry->l2_bitmap
> +	)
> +);
> +
> +#endif /* __PANTHOR_TRACE_H__ */
> +
> +#undef TRACE_INCLUDE_PATH
> +#define TRACE_INCLUDE_PATH .
> +#undef TRACE_INCLUDE_FILE
> +#define TRACE_INCLUDE_FILE panthor_trace
> +
> +#include <trace/define_trace.h>
>