Re: [PATCH i-g-t] tests/intel/kms_pm_dc: Detect frame drops via page-flip events

[Dibin Moolakadan Subrahmanian <dibin.moolakadan.subrahmanian@intel.com>]

On 7/9/2026 10:39 AM, Jeevan B wrote:
> The DC3CO frame-drop test currently waits for a vblank after committing
> a new framebuffer, which does not guarantee that the frame was actually
> presented.
>
> Switch to page flips and wait for the corresponding completion event,
> which confirms that the frame reached scanout. The test now alternates
> between two framebuffers using page flips, preserving the playback-like
> cadence needed to exercise DC3CO entry/exit transitions.
>
> Keep the existing vblank-gap validation, but derive the sequence number
> from the completed page flip instead of an independently waited vblank.
>
> Signed-off-by: Jeevan B <jeevan.b@intel.com>
> ---
>   tests/intel/kms_pm_dc.c | 69 +++++++++++++++++++++++++++++++----------
>   1 file changed, 52 insertions(+), 17 deletions(-)
>
> diff --git a/tests/intel/kms_pm_dc.c b/tests/intel/kms_pm_dc.c
> index ef53c5f96..da077a2dc 100644
> --- a/tests/intel/kms_pm_dc.c
> +++ b/tests/intel/kms_pm_dc.c
> @@ -362,30 +362,60 @@ static void test_dc3co_vpb_simulation(data_t *data)
>   	cleanup_dc3co_fbs(data);
>   }
>   
> -static uint32_t wait_for_next_vblank_seq(data_t *data)
> +struct dc3co_flip {
> +	bool done;
> +	unsigned int seq;
> +};
> +
> +static void dc3co_flip_handler(int fd, unsigned int seq, unsigned int tv_sec,
> +			       unsigned int tv_usec, void *user_data)
>   {
> -	drmVBlank wait = {};
> -	igt_crtc_t *crtc = data->output->pending_crtc;
> +	struct dc3co_flip *flip = user_data;
>   
> -	igt_assert_f(crtc, "No CRTC bound to output for vblank wait\n");
> +	flip->seq = seq;
> +	flip->done = true;
> +}
>   
> -	wait.request.type = kmstest_get_vbl_flag(crtc->crtc_index) |
> -						 DRM_VBLANK_RELATIVE |
> -						 DRM_VBLANK_NEXTONMISS;
> -	wait.request.sequence = 1;
> -	igt_assert_eq(drmWaitVBlank(data->drm_fd, &wait), 0);
> +static unsigned int dc3co_flip_and_wait(data_t *data, uint32_t crtc_id,
> +					uint32_t fb_id, int frame_time_us)
> +{
> +	drmEventContext evctx = {
> +		.version = 2,
> +		.page_flip_handler = dc3co_flip_handler,
> +	};
> +	struct dc3co_flip flip = {};
> +	struct pollfd pfd = {
> +		.fd = data->drm_fd,
> +		.events = POLLIN,
> +	};
> +	int timeout_ms = (DC3CO_MAX_VBLANK_GAP + 2) * frame_time_us / 1000;
> +
> +	if (timeout_ms < 50)
> +		timeout_ms = 50;
>   
> -	return wait.reply.sequence;
> +	igt_assert_eq(drmModePageFlip(data->drm_fd, crtc_id, fb_id,
> +				      DRM_MODE_PAGE_FLIP_EVENT, &flip), 0);
> +
> +	while (!flip.done) {
> +		igt_assert_f(poll(&pfd, 1, timeout_ms) > 0,
> +			     "Frame dropped: no page flip completion within %d ms "
> +			     "during DC3CO entry/exit\n", timeout_ms);
> +		igt_assert_eq(drmHandleEvent(data->drm_fd, &evctx), 0);
> +	}
> +
> +	return flip.seq;
>   }
>   
>   static void detect_dc3co_framedrop(data_t *data)
>   {
>   	igt_plane_t *primary;
> +	igt_crtc_t *crtc;
>   	uint32_t dc3co_prev_cnt;
>   	uint32_t dc3co_cur_cnt;
>   	uint32_t prev_vblank_seq = 0;
>   	uint32_t vblank_seq;
>   	uint32_t vblank_gap;
> +	int frame_time_us;
>   	int delay;
>   	int committed = 0;
>   	bool dc3co_after_target = false;
> @@ -393,25 +423,30 @@ static void detect_dc3co_framedrop(data_t *data)
>   
>   	igt_require_f(data->mode->vrefresh != 0, "Invalid vrefresh rate of 0\n");
>   
> +	crtc = data->output->pending_crtc;
> +	igt_assert_f(crtc, "No CRTC bound to output\n");
> +
>   	primary = igt_output_get_plane_type(data->output, DRM_PLANE_TYPE_PRIMARY);
> -	igt_plane_set_fb(primary, NULL);
> +
> +	igt_plane_set_fb(primary, &data->fb_rgb);
>   	igt_display_commit(&data->display);
>   
>   	dc3co_prev_cnt = igt_read_dc_counter(data->debugfs_fd, IGT_INTEL_CHECK_DC3CO);
>   
> -	delay = (int)(DC3CO_FRAME_DELAY_FACTOR * (1000000 / data->mode->vrefresh));
> +	frame_time_us = 1000000 / data->mode->vrefresh;
> +	delay = (int)(DC3CO_FRAME_DELAY_FACTOR * frame_time_us);
>   
>   	while (committed < DC3CO_VERIFY_COMMITS) {
>   		front = !front;
> -		igt_plane_set_fb(primary, front ? &data->fb_rgr : &data->fb_rgb);
> -		igt_display_commit(&data->display);
> -
> -		vblank_seq = wait_for_next_vblank_seq(data);
> +		vblank_seq = dc3co_flip_and_wait(data, crtc->crtc_id,
> +						 front ? data->fb_rgr.fb_id :
> +							 data->fb_rgb.fb_id,
> +						 frame_time_us);
>   		if (prev_vblank_seq) {
>   			vblank_gap = vblank_seq - prev_vblank_seq;
>   			igt_assert_f(igt_vblank_after(vblank_seq, prev_vblank_seq) &&
>   				     vblank_gap <= DC3CO_MAX_VBLANK_GAP,
> -				     "Unexpected vblank gap %u after commit %d (prev=%u, cur=%u)\n",
> +				     "Frame drop: unexpected vblank gap %u after commit %d (prev=%u, cur=%u)\n",
>   				     vblank_gap, committed + 1, prev_vblank_seq, vblank_seq);
>   		}
>   		prev_vblank_seq = vblank_seq;

Page flips fit video-playback simulation better than the vblank wait.
LGTM.
Reviewed-by: Dibin Moolakadan Subrahmanian <dibin.moolakadan.subrahmanian@intel.com>