Re: [PATCH v2] drm: document uAPI page-flip flags

[Pekka Paalanen <ppaalanen@gmail.com>]

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On Mon, 29 Aug 2022 15:40:01 +0000
Simon Ser <contact@emersion.fr> wrote:

> Document flags accepted by the page-flip and atomic IOCTLs.
> 
> v2 (Pekka):
> - Mention DRM_EVENT_FLIP_COMPLETE in DRM_MODE_PAGE_FLIP_EVENT docs.
> - Expand DRM_MODE_ATOMIC_NONBLOCK and DRM_MODE_ATOMIC_ALLOW_MODESET
>   description.
> 
> Signed-off-by: Simon Ser <contact@emersion.fr>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Pekka Paalanen <ppaalanen@gmail.com>
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> ---
>  include/uapi/drm/drm_mode.h | 60 ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 59 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index fa953309d9ce..fa26bda6ffb3 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -935,12 +935,31 @@ struct hdr_output_metadata {
>  	};
>  };
>  
> +/**
> + * DRM_MODE_PAGE_FLIP_EVENT
> + *
> + * Request that the kernel sends back a vblank event (see
> + * struct drm_event_vblank) with the &DRM_EVENT_FLIP_COMPLETE type when the
> + * page-flip is done.
> + */
>  #define DRM_MODE_PAGE_FLIP_EVENT 0x01
> +/**
> + * DRM_MODE_PAGE_FLIP_ASYNC
> + *
> + * Request that the page-flip is performed as soon as possible, ie. with no
> + * delay due to waiting for vblank. This may cause tearing to be visible on
> + * the screen.
> + */
>  #define DRM_MODE_PAGE_FLIP_ASYNC 0x02
>  #define DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE 0x4
>  #define DRM_MODE_PAGE_FLIP_TARGET_RELATIVE 0x8
>  #define DRM_MODE_PAGE_FLIP_TARGET (DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE | \
>  				   DRM_MODE_PAGE_FLIP_TARGET_RELATIVE)
> +/**
> + * DRM_MODE_PAGE_FLIP_FLAGS
> + *
> + * Bitmask of flags suitable for &drm_mode_crtc_page_flip_target.flags.
> + */
>  #define DRM_MODE_PAGE_FLIP_FLAGS (DRM_MODE_PAGE_FLIP_EVENT | \
>  				  DRM_MODE_PAGE_FLIP_ASYNC | \
>  				  DRM_MODE_PAGE_FLIP_TARGET)
> @@ -1034,11 +1053,50 @@ struct drm_mode_destroy_dumb {
>  	__u32 handle;
>  };
>  
> -/* page-flip flags are valid, plus: */
> +/**
> + * DRM_MODE_ATOMIC_TEST_ONLY
> + *
> + * Do not apply the atomic commit, instead check whether the hardware supports
> + * this configuration.
> + *
> + * See drm_mode_config_funcs.atomic_check for more details on test-only
> + * commits.
> + */
>  #define DRM_MODE_ATOMIC_TEST_ONLY 0x0100
> +/**
> + * DRM_MODE_ATOMIC_NONBLOCK
> + *
> + * Do not block while applying the atomic commit. The &DRM_IOCTL_MODE_ATOMIC
> + * IOCTL returns immediately instead of waiting for the changes to be applied
> + * in hardware. Note, the driver will still check that the update can be
> + * applied before retuning.
> + */
>  #define DRM_MODE_ATOMIC_NONBLOCK  0x0200
> +/**
> + * DRM_MODE_ATOMIC_ALLOW_MODESET
> + *
> + * Allow the update to result in temporary or transient visible artifacts while
> + * the update is being applied. Applying the update may also take significantly
> + * more time than a page flip. The visual artifacts will not appear after the
> + * update is completed.
> + *
> + * This flag must be set when the KMS update might cause visible artifacts.
> + * Without this flag such KMS update will return a EINVAL error. What kind of
> + * update may cause visible artifacts depends on the driver and the hardware.
> + * User-space that needs to know beforehand if an update might cause visible
> + * artifacts can use &DRM_MODE_ATOMIC_TEST_ONLY without
> + * &DRM_MODE_ATOMIC_ALLOW_MODESET to see if it fails.
> + *
> + * Visual artifacts are guaranteed to not appear when this flag is not set.

Hi Simon,

all this looks good to me, aside from the question of whether
ALLOW_MODESET should be talking about visual artifacts or only about
interrupting the video signal or something.


Thanks,
pq

> + */
>  #define DRM_MODE_ATOMIC_ALLOW_MODESET 0x0400
>  
> +/**
> + * DRM_MODE_ATOMIC_FLAGS
> + *
> + * Bitfield of flags accepted by the &DRM_IOCTL_MODE_ATOMIC IOCTL in
> + * &drm_mode_atomic.flags.
> + */
>  #define DRM_MODE_ATOMIC_FLAGS (\
>  		DRM_MODE_PAGE_FLIP_EVENT |\
>  		DRM_MODE_PAGE_FLIP_ASYNC |\


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