[PATCH] drm/i915: Raise RPS FUp Interrupt Limiter for GEN9LP above softmax (v2)

[kai.chen@intel.com]

From: Kai Chen <kai.chen@intel.com>

On GEN9LP, raise the RPS FUp Interrupt Limiter above softmax so that the
HW won't miss interrupt when requested max_freq is set back to RP0
value.
The (v2) is to explain a bit more detail background about the change in
the code.

Signed-off-by: Kai Chen <kai.chen@intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index d99e5fabe93c..6574696b83cb 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -6276,7 +6276,27 @@ static u32 intel_rps_limits(struct drm_i915_private *dev_priv, u8 val)
 	 * frequency, if the down threshold expires in that window we will not
 	 * receive a down interrupt. */
 	if (INTEL_GEN(dev_priv) >= 9) {
-		limits = (rps->max_freq_softlimit) << 23;
+		int max_freq = rps->max_freq_softlimit;
+		int rp0_freq = rps->rp0_freq;
+
+		if (IS_GEN9_LP(dev_priv) && (max_freq == rp0_freq))
+			/* For GEN9_LP, the HW seems insensitive to the RP FUp
+			 * interrupt limiter threshold by design. This symptom
+			 * is experienced in the IGT test (pm_rps): when the
+			 * test sets the max_freq back to RP0, the interrupt
+			 * limits register is also programmed to the max_freq
+			 * per design. But as a result, the actual freq is not
+			 * the max_freq detected. It is suggested (based on the
+			 * best test/tuning practice) to increase the upper
+			 * interrupt limiter just by 1 (16.6MHz) so that the HW
+			 * will generate an interrupt when we are near or just
+			 * below the upper limit.
+			 */
+
+			limits = (rps->max_freq_softlimit + 1) << 23;
+		else
+			limits = (rps->max_freq_softlimit) << 23;
+
 		if (val <= rps->min_freq_softlimit)
 			limits |= (rps->min_freq_softlimit) << 14;
 	} else {
-- 
2.17.1

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