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drm/i915/perf: workaround register corruption in OATAILPTR

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After having written the entire OA buffer with reports, the HW will
write again at the beginning of the OA buffer. It'll indicate it by
setting the WRAP bits in the OASTATUS register.

When a wrap happens and that at the end of the read vfunc we write the
OASTATUS register back to clear the REPORT_LOST bit, we sometimes see
that the OATAILPTR register is reset to a previous position on Gen8/9
(apparently not the case on Gen11+). This leads the next call to the
read vfunc to process reports we've already read. Because we've marked
those as read by clearing the reason & timestamp dwords, they're
discarded and a "Skipping spurious, invalid OA report" message is
emitted.

The workaround to avoid this OATAILPTR value reset seems to be to set
the wrap bits when writing back OASTATUS.

This change has no impact on userspace, it only avoids a bunch of
DRM_NOTE("Skipping spurious, invalid OA report\n") messages.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: 19f81df285 ("drm/i915/perf: Add OA unit support for Gen 8+")
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201117130124.829979-1-lionel.g.landwerlin@intel.com
(cherry picked from commit 059a0beb486344a577ff476acce75e69eab704be)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
This commit is contained in:
Lionel Landwerlin
2020-11-17 15:01:24 +02:00
committed by Rodrigo Vivi
parent 418baf2c28
commit 0305613dbc
2 changed files with 9 additions and 2 deletions
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9
drivers/gpu/drm/i915/i915_perf.c
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@@ -909,8 +909,13 @@ static int gen8_oa_read(struct i915_perf_stream *stream,
DRM_I915_PERF_RECORD_OA_REPORT_LOST);
if (ret)
return ret;
intel_uncore_write(uncore, oastatus_reg,
oastatus & ~GEN8_OASTATUS_REPORT_LOST);
intel_uncore_rmw(uncore, oastatus_reg,
GEN8_OASTATUS_COUNTER_OVERFLOW |
GEN8_OASTATUS_REPORT_LOST,
IS_GEN_RANGE(uncore->i915, 8, 10) ?
(GEN8_OASTATUS_HEAD_POINTER_WRAP |
GEN8_OASTATUS_TAIL_POINTER_WRAP) : 0);
}
return gen8_append_oa_reports(stream, buf, count, offset);