Bspec says:
"The mailbox response data may not account for memory read latency.
If the mailbox response data for level 0 is 0us, add 2 microseconds
to the result for each valid level."
This means we should only do the +2 in case wm[0] == 0, not always.
So split the sanitizing implementation from the WA implementation and
fix the WA implementation.
v2: Add Fixes tag (Maarten).
Fixes: 367294be7c25 ("drm/i915/gen9: Add 2us read latency to WM level")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Vandana Kannan <vandana.kannan@xxxxxxxxx>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_pm.c | 42 +++++++++++++++++++++--------------------
1 file changed, 22 insertions(+), 20 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 1968672..fe43044 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -2127,32 +2127,34 @@ static void intel_read_wm_latency(struct drm_device *dev, uint16_t wm[8])
GEN9_MEM_LATENCY_LEVEL_MASK;
/*
+ * If a level n (n > 1) has a 0us latency, all levels m (m >= n)
+ * need to be disabled. We make sure to sanitize the values out
+ * of the punit to satisfy this requirement.
+ */
+ for (level = 1; level <= max_level; level++) {
+ if (wm[level] == 0) {
+ for (i = level + 1; i <= max_level; i++)
+ wm[i] = 0;
+ break;
+ }
+ }
+
+ /*
* WaWmMemoryReadLatency:skl
*
* punit doesn't take into account the read latency so we need
- * to add 2us to the various latency levels we retrieve from
- * the punit.
- * - W0 is a bit special in that it's the only level that
- * can't be disabled if we want to have display working, so
- * we always add 2us there.
- * - For levels >=1, punit returns 0us latency when they are
- * disabled, so we respect that and don't add 2us then
- *
- * Additionally, if a level n (n > 1) has a 0us latency, all
- * levels m (m >= n) need to be disabled. We make sure to
- * sanitize the values out of the punit to satisfy this
- * requirement.
+ * to add 2us to the various latency levels we retrieve from the
+ * punit when level 0 response data us 0us.
*/
- wm[0] += 2;
- for (level = 1; level <= max_level; level++)
- if (wm[level] != 0)
+ if (wm[0] == 0) {
+ wm[0] += 2;
+ for (level = 1; level <= max_level; level++) {
+ if (wm[level] == 0)
+ break;
wm[level] += 2;
- else {
- for (i = level + 1; i <= max_level; i++)
- wm[i] = 0;
-
- break;
}
+ }
+
} else if (IS_HASWELL(dev) || IS_BROADWELL(dev)) {
uint64_t sskpd = I915_READ64(MCH_SSKPD);
--
2.7.4
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