From: Ryan Zhang <[email protected]> The first read of GPU_TIMESTAMP after the GPU has been idle can return a value that lags the real counter, while a read issued immediately after is accurate.
Userspace correlates this timestamp with the host clock, so a stale value shows up as skew between the device and host time domains and makes dEQP-VK.pipeline.monolithic.timestamp.calibrated.calibration_test fail whenever a query happens to hit a large first-read error. Signed-off-by: Ryan Zhang <[email protected]> Reviewed-by: Liviu Dudau <[email protected]> --- v2: - Added the r-b in commit msg. - Rebased on drm-misc-next to resolve conflict. - Moved the dummy read into panthor_gpu_get_timestamp() to align with the refactored timestamp query code on drm-misc-next. Note: The original v1 patch was based on v6.18 and applied cleanly there. Could we also port v1 into 6.18? drivers/gpu/drm/panthor/panthor_gpu.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/gpu/drm/panthor/panthor_gpu.c b/drivers/gpu/drm/panthor/panthor_gpu.c index a383b04f101e..b8df5663f04e 100644 --- a/drivers/gpu/drm/panthor/panthor_gpu.c +++ b/drivers/gpu/drm/panthor/panthor_gpu.c @@ -2,6 +2,7 @@ /* Copyright 2018 Marty E. Plummer <[email protected]> */ /* Copyright 2019 Linaro, Ltd., Rob Herring <[email protected]> */ /* Copyright 2019 Collabora ltd. */ +/* Copyright 2026 NXP */ #include <linux/bitfield.h> #include <linux/bitmap.h> @@ -470,6 +471,9 @@ void panthor_gpu_resume(struct panthor_device *ptdev) u64 panthor_gpu_get_timestamp(struct panthor_device *ptdev) { + /* Dummy read to avoid stale values. */ + gpu_read64_counter(ptdev->gpu->iomem, GPU_TIMESTAMP); + return gpu_read64_counter(ptdev->gpu->iomem, GPU_TIMESTAMP); } -- 2.43.0
