Re: [PATCH kernel 1/2] drm: Pass CRTC ID in userspace vblank events

[Sean Paul <seanpaul@chromium.org>]

On Tue, Apr 04, 2017 at 05:52:21PM +0100, Daniel Stone wrote:
> From: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
> 
> With the atomic API, it is possible that a single commit affects
> multiple crtcs. If the user requests an event with that commit, one
> event will be sent for each CRTC, but it is not possible to distinguish
> which crtc an event is for in user space. To solve this, the reserved
> field in struct drm_vblank_event is repurposed to include the crtc_id
> which the event is for.
> 
> The DRM_CAP_CRTC_IN_VBLANK_EVENT is added to allow userspace to query if
> the crtc field will be set properly.
> 
> [daniels: Rebased, using Maarten's forward-port.]
> 
> Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
> Signed-off-by: Daniel Stone <daniels@collabora.com>

Yeah, this seems like good use of the reserved field to me.

Reviewed-by: Sean Paul <seanpaul@chromium.org>


> Cc: Maarten Lankhorst <maarten.lankhorst@intel.com>
> ---
>  drivers/gpu/drm/drm_ioctl.c | 3 +++
>  drivers/gpu/drm/drm_irq.c   | 2 ++
>  include/uapi/drm/drm.h      | 3 ++-
>  3 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
> index 7d6deaa91281..0793e2da9d21 100644
> --- a/drivers/gpu/drm/drm_ioctl.c
> +++ b/drivers/gpu/drm/drm_ioctl.c
> @@ -286,6 +286,9 @@ static int drm_getcap(struct drm_device *dev, void *data, struct drm_file *file_
>  	case DRM_CAP_ADDFB2_MODIFIERS:
>  		req->value = dev->mode_config.allow_fb_modifiers;
>  		break;
> +	case DRM_CAP_CRTC_IN_VBLANK_EVENT:
> +		req->value = 1;
> +		break;
>  	default:
>  		return -EINVAL;
>  	}
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index dac1b2593cb1..8c866cac62dd 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -1026,6 +1026,7 @@ void drm_crtc_arm_vblank_event(struct drm_crtc *crtc,
>  
>  	e->pipe = pipe;
>  	e->event.sequence = drm_vblank_count(dev, pipe);
> +	e->event.crtc_id = crtc->base.id;
>  	list_add_tail(&e->base.link, &dev->vblank_event_list);
>  }
>  EXPORT_SYMBOL(drm_crtc_arm_vblank_event);
> @@ -1056,6 +1057,7 @@ void drm_crtc_send_vblank_event(struct drm_crtc *crtc,
>  		now = get_drm_timestamp();
>  	}
>  	e->pipe = pipe;
> +	e->event.crtc_id = crtc->base.id;
>  	send_vblank_event(dev, e, seq, &now);
>  }
>  EXPORT_SYMBOL(drm_crtc_send_vblank_event);
> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
> index b2c52843bc70..42d9f64ce416 100644
> --- a/include/uapi/drm/drm.h
> +++ b/include/uapi/drm/drm.h
> @@ -647,6 +647,7 @@ struct drm_gem_open {
>  #define DRM_CAP_CURSOR_HEIGHT		0x9
>  #define DRM_CAP_ADDFB2_MODIFIERS	0x10
>  #define DRM_CAP_PAGE_FLIP_TARGET	0x11
> +#define DRM_CAP_CRTC_IN_VBLANK_EVENT	0x12
>  
>  /** DRM_IOCTL_GET_CAP ioctl argument type */
>  struct drm_get_cap {
> @@ -851,7 +852,7 @@ struct drm_event_vblank {
>  	__u32 tv_sec;
>  	__u32 tv_usec;
>  	__u32 sequence;
> -	__u32 reserved;
> +	__u32 crtc_id; /* 0 on older kernels that do not support this */
>  };
>  
>  /* typedef area */
> -- 
> 2.11.0
> 
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-- 
Sean Paul, Software Engineer, Google / Chromium OS
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