Re: [PATCH 1/4] drm/panfrost: Add cycle counter job requirement

[Steven Price <steven.price@arm.com>]

On 27/05/2021 21:38, alyssa.rosenzweig@collabora.com wrote:
> From: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
> 
> Extend the Panfrost UABI with a new job requirement for cycle counters
> (and GPU timestamps, by extension). This requirement is used in
> userspace to implement ARB_shader_clock, an OpenGL extension reporting
> the GPU cycle count within a shader. The same mechanism will be required
> to implement timestamp queries as a "write value - timestamp" job.
> 
> We cannot enable cycle counters unconditionally, as enabling them
> increases GPU power consumption. They should be left off unless actually
> required by the application for profiling purposes.
> 
> Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
> ---
>  include/uapi/drm/panfrost_drm.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/drm/panfrost_drm.h b/include/uapi/drm/panfrost_drm.h
> index ec19db1ee..27e6cb941 100644
> --- a/include/uapi/drm/panfrost_drm.h
> +++ b/include/uapi/drm/panfrost_drm.h
> @@ -39,7 +39,8 @@ extern "C" {
>  #define DRM_IOCTL_PANFROST_PERFCNT_ENABLE	DRM_IOW(DRM_COMMAND_BASE + DRM_PANFROST_PERFCNT_ENABLE, struct drm_panfrost_perfcnt_enable)
>  #define DRM_IOCTL_PANFROST_PERFCNT_DUMP		DRM_IOW(DRM_COMMAND_BASE + DRM_PANFROST_PERFCNT_DUMP, struct drm_panfrost_perfcnt_dump)
>  
> -#define PANFROST_JD_REQ_FS (1 << 0)
> +#define PANFROST_JD_REQ_FS			(1 << 0)
> +#define PANFROST_JD_REQ_PERMON			(1 << 1)

As noted PERMON is a bit jargony but matches kbase. Another option to
aid with the bike shedding could be _REQ_CYCLE_COUNT as this is
requesting cycle counters (and timestamp propagation). But I don't mind
the colour of the shed as long as it doesn't leak... ;)

Thanks,

Steve

>  /**
>   * struct drm_panfrost_submit - ioctl argument for submitting commands to the 3D
>   * engine.
>