[PATCH] drm/i915/selftests: Disable live_pphwsp_runtime on graphics version 12

When a context is saved and then restored, the timer delta is
calculated using signed 32 bit arithmetic on hardware written
value to PPHWSP/LRC image and previously stored value, which use
unsigned types. This difference may become negative for version
12, due to hardware quirk on these platforms. This in turn,
would cause -EOVERFLOW to be thrown inside live_pphwsp_runtime
test.

Similar case has been observed [1] and addressed [2] already,
so follow suit and disable the test here as well.

[1] https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/13697
[2] "73782fc64793 (i915/gt/selftests: Disable lrc_timestamp test)"

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16521
Signed-off-by: Krzysztof Karas <[email protected]>
---
 drivers/gpu/drm/i915/gt/selftest_lrc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c b/drivers/gpu/drm/i915/gt/selftest_lrc.c
index 23f04f6f8fba..d5196ef4a1e5 100644
--- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
+++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
@@ -1955,6 +1955,13 @@ static int live_pphwsp_runtime(void *arg)
 	enum intel_engine_id id;
 	int err = 0;
 
+	/*
+	 * Gen12 (TGL/DG2) has a hardware quirk, where CTX_TIMESTAMP may
+	 * appear to go backwards, causing sporadic underflow detections.
+	 */
+	if (GRAPHICS_VER(gt->i915) == 12)
+		return 0;
+
 	/*
 	 * Check that cumulative context runtime as stored in the pphwsp[16]
 	 * is monotonic.
-- 
2.34.1