Re: [PATCH v6 3/7] drm/panthor: Add panthor perf initialization and termination

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

On Mon, 15 Dec 2025 17:14:49 +0000
Lukas Zapolskas <lukas.zapolskas@arm.com> wrote:

> Added the panthor_perf system initialization and unplug code to allow
> for the handling of userspace sessions to be added in follow-up
> patches.
> 
> Signed-off-by: Lukas Zapolskas <lukas.zapolskas@arm.com>
> Reviewed-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_device.c |  2 +
>  drivers/gpu/drm/panthor/panthor_device.h |  5 +-
>  drivers/gpu/drm/panthor/panthor_perf.c   | 63 +++++++++++++++++++++++-
>  drivers/gpu/drm/panthor/panthor_perf.h   |  1 +
>  4 files changed, 69 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
> index dc237da92340..3063ffbead45 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.c
> +++ b/drivers/gpu/drm/panthor/panthor_device.c
> @@ -120,6 +120,7 @@ void panthor_device_unplug(struct panthor_device *ptdev)
>  	/* Now, try to cleanly shutdown the GPU before the device resources
>  	 * get reclaimed.
>  	 */
> +	panthor_perf_unplug(ptdev);
>  	panthor_sched_unplug(ptdev);
>  	panthor_fw_unplug(ptdev);
>  	panthor_mmu_unplug(ptdev);
> @@ -323,6 +324,7 @@ int panthor_device_init(struct panthor_device *ptdev)
>  
>  err_disable_autosuspend:
>  	pm_runtime_dont_use_autosuspend(ptdev->base.dev);
> +	panthor_perf_unplug(ptdev);
>  
>  err_unplug_sched:
>  	panthor_sched_unplug(ptdev);
> diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
> index 64b0048de6ac..e1a6250cecc8 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.h
> +++ b/drivers/gpu/drm/panthor/panthor_device.h
> @@ -28,8 +28,8 @@ struct panthor_hw;
>  struct panthor_job;
>  struct panthor_mmu;
>  struct panthor_fw;
> -struct panthor_perfcnt;
>  struct panthor_pwr;
> +struct panthor_perf;
>  struct panthor_vm;
>  struct panthor_vm_pool;
>  
> @@ -160,6 +160,9 @@ struct panthor_device {
>  	/** @devfreq: Device frequency scaling management data. */
>  	struct panthor_devfreq *devfreq;
>  
> +	/** @perf: Performance counter management data. */
> +	struct panthor_perf *perf;
> +
>  	/** @unplug: Device unplug related fields. */
>  	struct {
>  		/** @lock: Lock used to serialize unplug operations. */
> diff --git a/drivers/gpu/drm/panthor/panthor_perf.c b/drivers/gpu/drm/panthor/panthor_perf.c
> index 842d62826ac3..3a65d6d326e8 100644
> --- a/drivers/gpu/drm/panthor/panthor_perf.c
> +++ b/drivers/gpu/drm/panthor/panthor_perf.c
> @@ -4,6 +4,7 @@
>  
>  #include <linux/bitops.h>
>  #include <drm/panthor_drm.h>
> +#include <drm/drm_print.h>
>  
>  #include "panthor_device.h"
>  #include "panthor_fw.h"
> @@ -22,6 +23,19 @@
>   */
>  #define PANTHOR_HW_COUNTER_SIZE (sizeof(u32))
>  
> +struct panthor_perf {
> +	/** @next_session: The ID of the next session. */
> +	u32 next_session;
> +
> +	/** @session_range: The number of sessions supported at a time. */
> +	struct xa_limit session_range;
> +
> +	/**
> +	 * @sessions: Global map of sessions, accessed by their ID.
> +	 */
> +	struct xarray sessions;

Unless there's a need to have global session ID (sessions can be shared
and accessed from different processes), I'd move the xarray to some
panthor_file_perf object and make this session ID per-FD. Actually, I'm
not even sure I see a use case for having more than one session
per-file, so it could even be just a panthor_perf_session pointer and a
lock in panthor_file:

struct panthor_file {
	...
	struct {
		struct mutex lock;
		struct panthor_perf_session *session;
	} perf;
};

If we want to restrict the total number of sessions, we can have an
atomic_t in panthor_perf, but I think what really matters is the
maximum number of active sessions, and I believe we already have a
counter for that (panthor_perf_sampler::enabled_clients).

> +};
> +
>  struct panthor_perf_counter_block {
>  	struct drm_panthor_perf_block_header header;
>  	u64 counters[];
> @@ -76,14 +90,61 @@ static void panthor_perf_info_init(struct panthor_device *const ptdev)
>   * panthor_perf_init - Initialize the performance counter subsystem.
>   * @ptdev: Panthor device
>   *
> + * The performance counters require the FW interface to be available to setup the
> + * sampling ringbuffers, so this must be called only after FW is initialized.
> + *
>   * Return: 0 on success, negative error code on failure.
>   */
>  int panthor_perf_init(struct panthor_device *ptdev)
>  {
> +	struct panthor_perf *perf __free(kfree) = NULL;
> +	int ret = 0;
> +
>  	if (!ptdev)
>  		return -EINVAL;
>  
>  	panthor_perf_info_init(ptdev);
>  
> -	return 0;
> +	perf = kzalloc(sizeof(*perf), GFP_KERNEL);
> +	if (ZERO_OR_NULL_PTR(perf))
> +		return -ENOMEM;
> +
> +	xa_init_flags(&perf->sessions, XA_FLAGS_ALLOC);
> +
> +	perf->session_range = (struct xa_limit) {
> +		.min = 0,
> +		.max = 1,
> +	};
> +
> +	drm_info(&ptdev->base, "Performance counter subsystem initialized");
> +
> +	ptdev->perf = no_free_ptr(perf);
> +
> +	return ret;
> +}
> +
> +/**
> + * panthor_perf_unplug - Terminate the performance counter subsystem.
> + * @ptdev: Panthor device.
> + *
> + * This function will terminate the performance counter control structures and any remaining
> + * sessions, after waiting for any pending interrupts.
> + */
> +void panthor_perf_unplug(struct panthor_device *ptdev)
> +{
> +	struct panthor_perf *perf = ptdev->perf;
> +
> +	if (!perf)
> +		return;
> +
> +	if (!xa_empty(&perf->sessions)) {
> +		drm_err(&ptdev->base,
> +			"Performance counter sessions active when unplugging the driver!");
> +	}
> +
> +	xa_destroy(&perf->sessions);
> +
> +	kfree(ptdev->perf);
> +
> +	ptdev->perf = NULL;
>  }
> diff --git a/drivers/gpu/drm/panthor/panthor_perf.h b/drivers/gpu/drm/panthor/panthor_perf.h
> index 3c32c24c164c..e4805727b9e7 100644
> --- a/drivers/gpu/drm/panthor/panthor_perf.h
> +++ b/drivers/gpu/drm/panthor/panthor_perf.h
> @@ -10,6 +10,7 @@
>  struct panthor_device;
>  
>  int panthor_perf_init(struct panthor_device *ptdev);
> +void panthor_perf_unplug(struct panthor_device *ptdev);
>  
>  #endif /* __PANTHOR_PERF_H__ */
>