Patch "drm/i915: Make RPS EI/thresholds multiple of 25 on SNB-BDW" has been added to the 4.5-stable tree

This is a note to let you know that I've just added the patch titled

drm/i915: Make RPS EI/thresholds multiple of 25 on SNB-BDW

to the 4.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     drm-i915-make-rps-ei-thresholds-multiple-of-25-on-snb-bdw.patch

and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <[email protected]>
Date: Wed, 20 Apr 2016 16:43:56 +0300
Subject: drm/i915: Make RPS EI/thresholds multiple of 25 on SNB-BDW
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From: Ville Syrjälä <[email protected]>

commit 4ea3959018d09edfa36a9e7b5ccdbd4ec4b99e49 upstream.

Somehow my SNB GT1 (Dell XPS 8300) gets very unhappy around GPU hangs if the RPS EI/thresholds aren't suitably aligned. It seems like scheduling/timer interupts stop working somehow and things get stuck eg. in usleep_range().

I bisected the problem down to
commit 8a5864377b12 ("drm/i915/skl: Restructured the gen6_set_rps_thresholds function") I observed that before all the values were at least multiples of 25,
but afterwards they are not. And rounding things up to the next multiple of 25 does seem to help, so lets' do that. I also tried roundup(..., 5) but that wasn't sufficient. Also I have no idea if we might need this sort of thing on gen9+ as well.

These are the original EI/thresholds:
LOW_POWER

  GEN6_RP_UP_EI          12500
  GEN6_RP_UP_THRESHOLD   11800
  GEN6_RP_DOWN_EI        25000

GEN6_RP_DOWN_THRESHOLD 21250
BETWEEN
GEN6_RP_UP_EI 10250
GEN6_RP_UP_THRESHOLD 9225
GEN6_RP_DOWN_EI 25000
GEN6_RP_DOWN_THRESHOLD 18750
HIGH_POWER
GEN6_RP_UP_EI 8000
GEN6_RP_UP_THRESHOLD 6800
GEN6_RP_DOWN_EI 25000
GEN6_RP_DOWN_THRESHOLD 15000

These are after 8a5864377b12:
LOW_POWER

  GEN6_RP_UP_EI          12500
  GEN6_RP_UP_THRESHOLD   11875
  GEN6_RP_DOWN_EI        25000

GEN6_RP_DOWN_THRESHOLD 21250
BETWEEN
GEN6_RP_UP_EI 10156
GEN6_RP_UP_THRESHOLD 9140
GEN6_RP_DOWN_EI 25000
GEN6_RP_DOWN_THRESHOLD 18750
HIGH_POWER
GEN6_RP_UP_EI 7812
GEN6_RP_UP_THRESHOLD 6640
GEN6_RP_DOWN_EI 25000
GEN6_RP_DOWN_THRESHOLD 15000

And these are what we have after this patch:
LOW_POWER

  GEN6_RP_UP_EI          12500
  GEN6_RP_UP_THRESHOLD   11875
  GEN6_RP_DOWN_EI        25000

GEN6_RP_DOWN_THRESHOLD 21250
BETWEEN
GEN6_RP_UP_EI 10175
GEN6_RP_UP_THRESHOLD 9150
GEN6_RP_DOWN_EI 25000
GEN6_RP_DOWN_THRESHOLD 18750
HIGH_POWER
GEN6_RP_UP_EI 7825
GEN6_RP_UP_THRESHOLD 6650
GEN6_RP_DOWN_EI 25000
GEN6_RP_DOWN_THRESHOLD 15000

Cc: Akash Goel <[email protected]>
Cc: Chris Wilson <[email protected]>
Testcase: igt/kms_pipe_crc_basic/hang-read-crc-pipe-B

---
 drivers/gpu/drm/i915/i915_reg.h |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

@@ -2898,7 +2898,14 @@ enum skl_disp_power_wells {
 #define GEN6_RP_STATE_CAP	_MMIO(MCHBAR_MIRROR_BASE_SNB + 0x5998)
 #define BXT_RP_STATE_CAP        _MMIO(0x138170)
 
-#define INTERVAL_1_28_US(us)	(((us) * 100) >> 7)
+/*
+ * Make these a multiple of magic 25 to avoid SNB (eg. Dell XPS
+ * 8300) freezing up around GPU hangs. Looks as if even
+ * scheduling/timer interrupts start misbehaving if the RPS
+ * EI/thresholds are "bad", leading to a very sluggish or even
+ * frozen machine.
+ */
+#define INTERVAL_1_28_US(us)	roundup(((us) * 100) >> 7, 25)
 #define INTERVAL_1_33_US(us)	(((us) * 3)   >> 2)
 #define INTERVAL_0_833_US(us)	(((us) * 6) / 5)
 #define GT_INTERVAL_FROM_US(dev_priv, us) (IS_GEN9(dev_priv) ? \

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/gpiolib-acpi-duplicate-con_id-string-when-adding-it-to-the-crs-lookup-list.patch queue-4.5/drm-i915-make-rps-ei-thresholds-multiple-of-25-on-snb-bdw.patch queue-4.5/drm-i915-ddi-fix-edp-vdd-handling-during-booting-and-suspend-resume.patch queue-4.5/drm-i915-fix-edp-low-vswing-for-broadwell.patch queue-4.5/drm-i915-fix-system-resume-if-pci-device-remained-enabled.patch queue-4.5/drm-i915-avoid-stalling-on-pending-flips-for-legacy-cursor-updates.patch queue-4.5/drm-i915-fake-hdmi-live-status.patch