Re: [PATCH] drm: add capability DRM_CAP_ASYNC_UPDATE

[Ville Syrjälä]

On Fri, Nov 23, 2018 at 07:53:26PM -0200, Helen Koike wrote:
> Allow userspace to identify if the driver supports async update.

And what exactly is an "async update"?

I keep asking people to come up with the a better name for this, and to
document what it actually means. Recently I've been think we should
maybe just adopt the vulkan terminology (immediate/fifo/mailbox) to
avoid introducing yet another set of names for the same thing. We'd
still want to document things properly though.

> 
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
> [prepared for upstream]
> Signed-off-by: Helen Koike <helen.koike@xxxxxxxxxxxxx>
> 
> ---
> Hi,
> 
> This patch introduces the ASYNC_UPDATE cap, which originated from the
> discussion regarding DRM_MODE_ATOMIC_AMEND on [1], to allow user to
> figure that async_update exists.
> 
> This was tested using a small program that exercises the uAPI for easy
> sanity testing. The program was created by Alexandros and modified by
> Enric to test the capability flag [2].
> 
> The test worked on a rockchip Ficus v1.1 board on top of mainline plus
> the patch to update cursors asynchronously through atomic plus the patch
> that introduces the ATOMIC_AMEND flag for the drm/rockchip driver.
> 
> To test, just build the program and use the --atomic flag to use the cursor
> plane with the ATOMIC_AMEND flag. E.g.
> 
>   drm_cursor --atomic
> 
> [1] https://patchwork.freedesktop.org/patch/243088/
> [2] https://gitlab.collabora.com/eballetbo/drm-cursor/commits/async-capability
> 
> Thanks
> Helen
> 
> 
>  drivers/gpu/drm/drm_ioctl.c | 11 +++++++++++
>  include/uapi/drm/drm.h      |  1 +
>  2 files changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
> index 94bd872d56c4..4a7e0f874171 100644
> --- a/drivers/gpu/drm/drm_ioctl.c
> +++ b/drivers/gpu/drm/drm_ioctl.c
> @@ -31,6 +31,7 @@
>  #include <drm/drm_ioctl.h>
>  #include <drm/drmP.h>
>  #include <drm/drm_auth.h>
> +#include <drm/drm_modeset_helper_vtables.h>
>  #include "drm_legacy.h"
>  #include "drm_internal.h"
>  #include "drm_crtc_internal.h"
> @@ -229,6 +230,7 @@ static int drm_getcap(struct drm_device *dev, void *data, struct drm_file *file_
>  {
>  	struct drm_get_cap *req = data;
>  	struct drm_crtc *crtc;
> +	struct drm_plane *plane;
>  
>  	req->value = 0;
>  
> @@ -292,6 +294,15 @@ static int drm_getcap(struct drm_device *dev, void *data, struct drm_file *file_
>  	case DRM_CAP_CRTC_IN_VBLANK_EVENT:
>  		req->value = 1;
>  		break;
> +	case DRM_CAP_ASYNC_UPDATE:
> +		req->value = 1;
> +		list_for_each_entry(plane, &dev->mode_config.plane_list, head) {
> +			if (!plane->helper_private->atomic_async_update) {
> +				req->value = 0;
> +				break;
> +			}
> +		}
> +		break;
>  	default:
>  		return -EINVAL;
>  	}
> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
> index 300f336633f2..ff01540cbb1d 100644
> --- a/include/uapi/drm/drm.h
> +++ b/include/uapi/drm/drm.h
> @@ -649,6 +649,7 @@ struct drm_gem_open {
>  #define DRM_CAP_PAGE_FLIP_TARGET	0x11
>  #define DRM_CAP_CRTC_IN_VBLANK_EVENT	0x12
>  #define DRM_CAP_SYNCOBJ		0x13
> +#define DRM_CAP_ASYNC_UPDATE		0x14
>  
>  /** DRM_IOCTL_GET_CAP ioctl argument type */
>  struct drm_get_cap {
> -- 
> 2.19.1
> 
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-- 
Ville Syrjälä
Intel