Re: [PATCH i-g-t 2/2] tests/kms_setmode: Disable CPU deep sleep for accurate vblank timestamps

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, May 20, 2026 at 02:46:26PM +0800, Jason-JH Lin wrote:
> Use igt_disable_cpu_deep_sleep() to prevent CPU wakeup latency that
> affects vblank timestamp acquisition.
> 
> This addresses vblank timing stability issues on MediaTek platforms
> where CPU entering idle states can cause ~200us timestamp jitter and
> test failures.

Can't you fix the kernel to generate accurate timestamps?

> 
> Signed-off-by: Jason-JH Lin <jason-jh.lin@mediatek.com>
> ---
>  tests/kms_setmode.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/tests/kms_setmode.c b/tests/kms_setmode.c
> index 1f2849bc26cf..40e79ab95ae7 100644
> --- a/tests/kms_setmode.c
> +++ b/tests/kms_setmode.c
> @@ -1060,6 +1060,9 @@ int igt_main_args("det:", NULL, help_str, opt_handler, NULL)
>  		igt_require(drm_resources);
>  
>  		max_dotclock = igt_get_max_dotclock(drm_fd);
> +
> +		/* Disable CPU deep sleep to ensure stable vblank timing */
> +		igt_disable_cpu_deep_sleep(drm_fd, true);
>  	}
>  
>  	for (i = 0; i < ARRAY_SIZE(tests); i++) {
> @@ -1075,6 +1078,9 @@ int igt_main_args("det:", NULL, help_str, opt_handler, NULL)
>  	}
>  
>  	igt_fixture() {
> +		/* Restore CPU idle states */
> +		igt_disable_cpu_deep_sleep(drm_fd, false);
> +
>  		drmModeFreeResources(drm_resources);
>  		drm_close_driver(drm_fd);
>  	}
> -- 
> 2.43.0

-- 
Ville Syrjälä
Intel