[Intel-gfx] [PATCH 1/2] drm/i915/perf: Subtract gtt_offset from hw_tail

[Ashutosh Dixit]

The code in oa_buffer_check_unlocked() is correct only if the OA buffer is
16 MB aligned (which seems to be the case today in i915). However when the
16 MB alignment is dropped, when we "Subtract partial amount off the tail",
the "& (OA_BUFFER_SIZE - 1)" operation in OA_TAKEN() will result in an
incorrect hw_tail value.

Therefore hw_tail must be brought to the same base as head and read_tail
prior to OA_TAKEN by subtracting gtt_offset from hw_tail.

Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
---
 drivers/gpu/drm/i915/i915_perf.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index 49c6f1ff11284..f7888a44d1284 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -565,6 +565,7 @@ static bool oa_buffer_check_unlocked(struct i915_perf_stream *stream)
 	partial_report_size %= report_size;
 
 	/* Subtract partial amount off the tail */
+	hw_tail -= gtt_offset;
 	hw_tail = OA_TAKEN(hw_tail, partial_report_size);
 
 	/* NB: The head we observe here might effectively be a little
-- 
2.41.0