Re: [PATCH i-g-t v5 1/3] lib/igt_kms: Add helper to return vblank timestamp and sequence

[Jani Nikula <jani.nikula@intel.com>]

On Wed, 26 Aug 2026, Naladala Ramanaidu <ramanaidu.naladala@intel.com> wrote:
> Add a utility that waits for the next vertical blanking interval on a
> specified CRTC and returns the timestamp and sequence number reported
> by the kernel for that event.
>
> Several tests need access not only to vblank synchronization but also
> to the exact timing information associated with the completed vblank.
> Having a common helper avoids repeating the same wait and timestamp
> extraction.
>
> Assisted-by: GitHub Copilot:Claude Opus 4.6
> Signed-off-by: Naladala Ramanaidu <ramanaidu.naladala@intel.com>
> ---
>  lib/igt_kms.c | 25 +++++++++++++++++++++++++
>  lib/igt_kms.h |  1 +
>  2 files changed, 26 insertions(+)
>
> diff --git a/lib/igt_kms.c b/lib/igt_kms.c
> index 42cc7c3bd..cd4783db9 100644
> --- a/lib/igt_kms.c
> +++ b/lib/igt_kms.c
> @@ -5876,6 +5876,31 @@ void igt_wait_for_vblank_count(igt_crtc_t *crtc, int count)
>  	igt_assert(__igt_vblank_wait(crtc->display->drm_fd, crtc->crtc_index, count) == 0);
>  }
>  
> +/**
> + * igt_wait_for_vblank_ts_seq:
> + * @crtc: the CRTC.
> + * @ts_ns: returns the vblank timestamp in nanoseconds.
> + * @seq: returns the vblank sequence number.
> + *
> + * Waits for the next vertical blank interval on @crtc and hands back the
> + * timestamp and the sequence number.
> + */
> +void igt_wait_for_vblank_ts_seq(igt_crtc_t *crtc, uint64_t *ts_ns, unsigned int *seq)
> +{
> +	drmVBlank wait_vbl = {
> +		.request.type = DRM_VBLANK_RELATIVE | igt_crtc_get_vbl_flag(crtc),
> +		.request.sequence = 1,
> +	};
> +
> +	do_or_die(drmWaitVBlank(crtc->display->drm_fd, &wait_vbl));
> +
> +	if (ts_ns)
> +		*ts_ns = wait_vbl.reply.tval_sec * NSEC_PER_SEC +
> +			 wait_vbl.reply.tval_usec * NSEC_PER_USEC;
> +	if (seq)
> +		*seq = wait_vbl.reply.sequence;
> +}

Gut feeling says it's probably better to extend __igt_vblank_wait() and
make this a thin wrapper around that.

> +
>  /**
>   * igt_wait_for_vblank:
>   * @drm_fd: A drm file descriptor
> diff --git a/lib/igt_kms.h b/lib/igt_kms.h
> index 8d4d14847..8d1928af6 100644
> --- a/lib/igt_kms.h
> +++ b/lib/igt_kms.h
> @@ -652,6 +652,7 @@ static inline bool igt_plane_has_rotation(igt_plane_t *plane, igt_rotation_t rot
>  const char *igt_plane_rotation_name(igt_rotation_t rotation);
>  
>  void igt_wait_for_vblank(igt_crtc_t *crtc);
> +void igt_wait_for_vblank_ts_seq(igt_crtc_t *crtc, uint64_t *ts_ns, unsigned int *seq);
>  void igt_wait_for_vblank_count(igt_crtc_t *crtc, int count);
>  
>  /**

-- 
Jani Nikula, Intel