[PATCH] i915: pm: Be less agressive with clockfreq changes on Bay Trail

[Hans de Goede]

Bay Trail devices are known to hang when changing the frequency often,
this is discussed in great length in:
https://bugzilla.kernel.org/show_bug.cgi?id=109051

Commit 6067a27d1f01 ("drm/i915: Avoid tweaking evaluation thresholds
on Baytrail v3") is an attempt to workaround this. Several users in
bko109051 report that an earlier version of this patch, v1:
https://bugzilla.kernel.org/attachment.cgi?id=251471

Works better for them and they still see hangs with the merged v3.

Comparing the 2 versions shows that they are indeed not equivalent,
v1 not only skips writing the GEN6_RP* registers from valleyview_set_rps,
as v3 does. It also contained these modifications to i915_irq.c:

     if (pm_iir & GEN6_PM_RP_DOWN_EI_EXPIRED) {
         if (!vlv_c0_above(dev_priv,
                   &dev_priv->rps.down_ei, &now,
-                  dev_priv->rps.down_threshold))
+                  VLV_RP_DOWN_EI_THRESHOLD))
             events |= GEN6_PM_RP_DOWN_THRESHOLD;
         dev_priv->rps.down_ei = now;
     }

     if (pm_iir & GEN6_PM_RP_UP_EI_EXPIRED) {
         if (vlv_c0_above(dev_priv,
                  &dev_priv->rps.up_ei, &now,
-                 dev_priv->rps.up_threshold))
+                 VLV_RP_UP_EI_THRESHOLD))
             events |= GEN6_PM_RP_UP_THRESHOLD;
         dev_priv->rps.up_ei = now;
     }

Which use less aggressive up/down thresholds, which results in less
GEN6_PM_RP_*_THRESHOLD events and thus in less calls to intel_set_rps() ->
valleyview_set_rps() -> vlv_punit_write(PUNIT_REG_GPU_FREQ_REQ).
With the last call being the likely cause of the hang.

This commit hardcodes the threshold_up and _down values for Bay Trail to
less aggressive values, reducing the amount of clock frequency changes,
thus avoiding the hangs some people are still seeing with the merged fix.

Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=109051
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/i915/i915_reg.h | 3 +++
 drivers/gpu/drm/i915/intel_pm.c | 5 ++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 68a58cce6ab1..2561af075ebb 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -1355,6 +1355,9 @@ enum i915_power_well_id {
 #define 	VLV_BIAS_CPU_125_SOC_875 (6 << 2)
 #define 	CHV_BIAS_CPU_50_SOC_50 (3 << 2)
 
+#define VLV_RP_UP_EI_THRESHOLD			90
+#define VLV_RP_DOWN_EI_THRESHOLD		70
+
 /* vlv2 north clock has */
 #define CCK_FUSE_REG				0x8
 #define  CCK_FUSE_HPLL_FREQ_MASK		0x3
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 01966b89be14..177b6caa0a38 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -6096,8 +6096,11 @@ static void gen6_set_rps_thresholds(struct drm_i915_private *dev_priv, u8 val)
 	/* When byt can survive without system hang with dynamic
 	 * sw freq adjustments, this restriction can be lifted.
 	 */
-	if (IS_VALLEYVIEW(dev_priv))
+	if (IS_VALLEYVIEW(dev_priv)) {
+		threshold_up = VLV_RP_UP_EI_THRESHOLD;
+		threshold_down = VLV_RP_DOWN_EI_THRESHOLD;
 		goto skip_hw_write;
+	}
 
 	I915_WRITE(GEN6_RP_UP_EI,
 		   GT_INTERVAL_FROM_US(dev_priv, ei_up));
-- 
2.14.3