Re: [PATCH v10 3/4] drm/panthor: Add tracepoint for hardware utilisation changes

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

On Fri, 16 Jan 2026 13:57:32 +0100
Nicolas Frattaroli <nicolas.frattaroli@collabora.com> wrote:

> Mali GPUs have three registers that indicate which parts of the hardware
> are powered at any moment. These take the form of bitmaps. In the case
> of SHADER_READY for example, a high bit indicates that the shader core
> corresponding to that bit index is powered on. 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 _READY registers will contain new interesting data. During
> power transitions, the GPU_IRQ_POWER_CHANGED interrupt will fire, and
> the registers will likewise contain potentially changed data.
> 
> 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
> _READY registers and corresponding interrupts are already available in
> v9 and onwards.
> 
> Expose the data 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 powered shader core, measuring when hardware
> is allowed to go to a powered off state again, and so on.
> 
> The registration/unregistration functions for the tracepoint go through
> a wrapper in panthor_hw.c, so that v14+ can implement the same
> tracepoint by adding its hardware specific IRQ on/off callbacks to the
> panthor_hw.ops member.
> 
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_gpu.c   | 28 +++++++++++++++
>  drivers/gpu/drm/panthor/panthor_gpu.h   |  2 ++
>  drivers/gpu/drm/panthor/panthor_hw.c    | 62 +++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/panthor/panthor_hw.h    |  8 +++++
>  drivers/gpu/drm/panthor/panthor_trace.h | 58 ++++++++++++++++++++++++++++++
>  5 files changed, 158 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_gpu.c b/drivers/gpu/drm/panthor/panthor_gpu.c
> index 9304469a711a..2ab444ee8c71 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.
>   */
> @@ -48,6 +51,9 @@ struct panthor_gpu {
>  	 GPU_IRQ_RESET_COMPLETED | \
>  	 GPU_IRQ_CLEAN_CACHES_COMPLETED)
>  
> +#define GPU_POWER_INTERRUPTS_MASK	\
> +	(GPU_IRQ_POWER_CHANGED | GPU_IRQ_POWER_CHANGED_ALL)
> +
>  static void panthor_gpu_coherency_set(struct panthor_device *ptdev)
>  {
>  	gpu_write(ptdev, GPU_COHERENCY_PROTOCOL,
> @@ -80,6 +86,12 @@ static void panthor_gpu_irq_handler(struct panthor_device *ptdev, u32 status)
>  {
>  	gpu_write(ptdev, GPU_INT_CLEAR, status);
>  
> +	if (tracepoint_enabled(gpu_power_status) && (status & GPU_POWER_INTERRUPTS_MASK))
> +		trace_gpu_power_status(ptdev->base.dev,
> +				       gpu_read64(ptdev, SHADER_READY),
> +				       gpu_read64(ptdev, TILER_READY),
> +				       gpu_read64(ptdev, L2_READY));
> +
>  	if (status & GPU_IRQ_FAULT) {
>  		u32 fault_status = gpu_read(ptdev, GPU_FAULT_STATUS);
>  		u64 address = gpu_read64(ptdev, GPU_FAULT_ADDR);
> @@ -157,6 +169,22 @@ int panthor_gpu_init(struct panthor_device *ptdev)
>  	return 0;
>  }
>  
> +int panthor_gpu_power_changed_on(struct panthor_device *ptdev)
> +{
> +	guard(pm_runtime_active)(ptdev->base.dev);
> +
> +	panthor_gpu_irq_enable_events(&ptdev->gpu->irq, GPU_POWER_INTERRUPTS_MASK);
> +
> +	return 0;
> +}
> +
> +void panthor_gpu_power_changed_off(struct panthor_device *ptdev)
> +{
> +	guard(pm_runtime_active)(ptdev->base.dev);
> +
> +	panthor_gpu_irq_disable_events(&ptdev->gpu->irq, GPU_POWER_INTERRUPTS_MASK);
> +}
> +
>  /**
>   * panthor_gpu_block_power_off() - Power-off a specific block of the GPU
>   * @ptdev: Device.
> diff --git a/drivers/gpu/drm/panthor/panthor_gpu.h b/drivers/gpu/drm/panthor/panthor_gpu.h
> index 12e66f48ced1..12c263a39928 100644
> --- a/drivers/gpu/drm/panthor/panthor_gpu.h
> +++ b/drivers/gpu/drm/panthor/panthor_gpu.h
> @@ -51,5 +51,7 @@ int panthor_gpu_l2_power_on(struct panthor_device *ptdev);
>  int panthor_gpu_flush_caches(struct panthor_device *ptdev,
>  			     u32 l2, u32 lsc, u32 other);
>  int panthor_gpu_soft_reset(struct panthor_device *ptdev);
> +void panthor_gpu_power_changed_off(struct panthor_device *ptdev);
> +int panthor_gpu_power_changed_on(struct panthor_device *ptdev);
>  
>  #endif
> diff --git a/drivers/gpu/drm/panthor/panthor_hw.c b/drivers/gpu/drm/panthor/panthor_hw.c
> index 80c521784cd3..d135aa6724fa 100644
> --- a/drivers/gpu/drm/panthor/panthor_hw.c
> +++ b/drivers/gpu/drm/panthor/panthor_hw.c
> @@ -2,6 +2,8 @@
>  /* Copyright 2025 ARM Limited. All rights reserved. */
>  
>  #include <linux/nvmem-consumer.h>
> +#include <linux/platform_device.h>
> +
>  #include <drm/drm_print.h>
>  
>  #include "panthor_device.h"
> @@ -30,6 +32,8 @@ static struct panthor_hw panthor_hw_arch_v10 = {
>  		.soft_reset = panthor_gpu_soft_reset,
>  		.l2_power_off = panthor_gpu_l2_power_off,
>  		.l2_power_on = panthor_gpu_l2_power_on,
> +		.power_changed_off = panthor_gpu_power_changed_off,
> +		.power_changed_on = panthor_gpu_power_changed_on,
>  	},
>  };
>  
> @@ -54,6 +58,64 @@ static struct panthor_hw_entry panthor_hw_match[] = {
>  	},
>  };
>  
> +static int panthor_hw_set_power_tracing(struct device *dev, void *data)
> +{
> +	struct panthor_device *ptdev = dev_get_drvdata(dev);
> +
> +	if (!ptdev)
> +		return -ENODEV;
> +
> +	if (!ptdev->hw)
> +		return 0;
> +
> +	if (data) {
> +		if (ptdev->hw->ops.power_changed_on)
> +			return ptdev->hw->ops.power_changed_on(ptdev);
> +	} else {
> +		if (ptdev->hw->ops.power_changed_off)
> +			ptdev->hw->ops.power_changed_off(ptdev);
> +	}
> +
> +	return 0;
> +}

nit: since you've already exposed the power transition monitoring
through two different callbacks, could we also do the same here, with
two panthor_hw_power_tracing_{on,off}() functions which ignore the
data (not a huge fan of this bool->pointer cast).

static int panthor_hw_power_tracing_on(struct device *dev, void *data)
{
	struct panthor_device *ptdev = dev_get_drvdata(dev);

	if (!ptdev)
		return -ENODEV;

	if (ptdev->hw && ptdev->hw->ops.power_changed_on)
		return ptdev->hw->ops.power_changed_on(ptdev);

	return 0;
}

static int panthor_hw_power_tracing_off(struct device *dev, void *data)
{
	struct panthor_device *ptdev = dev_get_drvdata(dev);

	if (!ptdev)
		return -ENODEV;

	if (ptdev->hw && ptdev->hw->ops.power_changed_off)
		return ptdev->hw->ops.power_changed_off(ptdev);

	return 0;
}

Feel free to ignore, this patch is

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

regardless.

> +
> +int panthor_hw_power_status_register(void)
> +{
> +	struct device_driver *drv;
> +	int ret;
> +
> +	drv = driver_find("panthor", &platform_bus_type);
> +	if (!drv)
> +		return -ENODEV;
> +
> +	ret = driver_for_each_device(drv, NULL, (void *)true,
> +				     panthor_hw_set_power_tracing);
> +
> +	return ret;
> +}
> +
> +void panthor_hw_power_status_unregister(void)
> +{
> +	struct device_driver *drv;
> +	int ret;
> +
> +	drv = driver_find("panthor", &platform_bus_type);
> +	if (!drv)
> +		return;
> +
> +	ret = driver_for_each_device(drv, NULL, NULL, panthor_hw_set_power_tracing);
> +
> +	/*
> +	 * Ideally, it'd be possible to ask driver_for_each_device to hand us
> +	 * another "start" to keep going after the failing device, but it
> +	 * doesn't do that. Minor inconvenience in what is probably a bad day
> +	 * on the computer already though.
> +	 */
> +	if (ret)
> +		pr_warn("Couldn't mask power IRQ for at least one device: %pe\n",
> +			ERR_PTR(ret));
> +}
> +
>  static char *get_gpu_model_name(struct panthor_device *ptdev)
>  {
>  	const u32 gpu_id = ptdev->gpu_info.gpu_id;
> diff --git a/drivers/gpu/drm/panthor/panthor_hw.h b/drivers/gpu/drm/panthor/panthor_hw.h
> index 56c68c1e9c26..2c28aea82841 100644
> --- a/drivers/gpu/drm/panthor/panthor_hw.h
> +++ b/drivers/gpu/drm/panthor/panthor_hw.h
> @@ -19,6 +19,12 @@ struct panthor_hw_ops {
>  
>  	/** @l2_power_on: L2 power on function pointer */
>  	int (*l2_power_on)(struct panthor_device *ptdev);
> +
> +	/** @power_changed_on: Start listening to power change IRQs */
> +	int (*power_changed_on)(struct panthor_device *ptdev);
> +
> +	/** @power_changed_off: Stop listening to power change IRQs */
> +	void (*power_changed_off)(struct panthor_device *ptdev);
>  };
>  
>  /**
> @@ -32,6 +38,8 @@ struct panthor_hw {
>  };
>  
>  int panthor_hw_init(struct panthor_device *ptdev);
> +int panthor_hw_power_status_register(void);
> +void panthor_hw_power_status_unregister(void);
>  
>  static inline int panthor_hw_soft_reset(struct panthor_device *ptdev)
>  {
> diff --git a/drivers/gpu/drm/panthor/panthor_trace.h b/drivers/gpu/drm/panthor/panthor_trace.h
> new file mode 100644
> index 000000000000..5bd420894745
> --- /dev/null
> +++ b/drivers/gpu/drm/panthor/panthor_trace.h
> @@ -0,0 +1,58 @@
> +/* 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>
> +
> +#include "panthor_hw.h"
> +
> +/**
> + * gpu_power_status - called whenever parts of GPU hardware are turned on or off
> + * @dev: pointer to the &struct device, for printing the device name
> + * @shader_bitmap: bitmap where a high bit indicates the shader core at a given
> + *                 bit index is on, and a low bit indicates a shader core is
> + *                 either powered off or absent
> + * @tiler_bitmap: bitmap where a high bit indicates the tiler unit at a given
> + *                bit index is on, and a low bit indicates a tiler unit is
> + *                either powered off or absent
> + * @l2_bitmap: bitmap where a high bit indicates the L2 cache at a given bit
> + *             index is on, and a low bit indicates the L2 cache is either
> + *             powered off or absent
> + */
> +TRACE_EVENT_FN(gpu_power_status,
> +	TP_PROTO(const struct device *dev, u64 shader_bitmap, u64 tiler_bitmap,
> +		 u64 l2_bitmap),
> +	TP_ARGS(dev, shader_bitmap, tiler_bitmap, l2_bitmap),
> +	TP_STRUCT__entry(
> +		__string(dev_name, dev_name(dev))
> +		__field(u64, shader_bitmap)
> +		__field(u64, tiler_bitmap)
> +		__field(u64, l2_bitmap)
> +	),
> +	TP_fast_assign(
> +		__assign_str(dev_name);
> +		__entry->shader_bitmap	= shader_bitmap;
> +		__entry->tiler_bitmap	= tiler_bitmap;
> +		__entry->l2_bitmap	= l2_bitmap;
> +	),
> +	TP_printk("%s: shader_bitmap=0x%llx tiler_bitmap=0x%llx l2_bitmap=0x%llx",
> +		  __get_str(dev_name), __entry->shader_bitmap, __entry->tiler_bitmap,
> +		  __entry->l2_bitmap
> +	),
> +	panthor_hw_power_status_register, panthor_hw_power_status_unregister
> +);
> +
> +#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>
>