drm/i915: Clean up multi-threaded forcewake patch

We learned that the ECOBUS register was inside the GT power well, and
so *did* need force wake to be read, so it gets removed from the list
of 'doesn't need force wake' registers.

That means the code reading ECOBUS after forcing the mt_force_wake
function to be called needs to use I915_READ_NOTRACE; it doesn't need
to do more force wake fun as it's already done it manually.

This also adds a comment explaining why the MT forcewake testing code
only needs to call mt_forcewake_get/put and not disable RC6 manually
-- the ECOBUS read will return 0 if the device is in RC6 and isn't
using MT forcewake, causing the test to work correctly.

Signed-off-by: Keith Packard <keithp@keithp.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>

3 files changed, 8 insertions, 10 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 22c8ab70db2c..8f7187915b0d 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -923,13 +923,6 @@ MODULE_AUTHOR(DRIVER_AUTHOR);
 MODULE_DESCRIPTION(DRIVER_DESC);
 MODULE_LICENSE("GPL and additional rights");
 
-/* We give fast paths for the really cool registers */
-#define NEEDS_FORCE_WAKE(dev_priv, reg) \
-        (((dev_priv)->info->gen >= 6) && \
-         ((reg) < 0x40000) &&            \
-         ((reg) != FORCEWAKE) &&         \
-         ((reg) != ECOBUS))
-
 #define __i915_read(x, y) \
 u##x i915_read##x(struct drm_i915_private *dev_priv, u32 reg) { \
         u##x val = 0; \
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 505af3f64a07..621840c05f0c 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1364,8 +1364,7 @@ void __gen6_gt_wait_for_fifo(struct drm_i915_private *dev_priv);
 #define NEEDS_FORCE_WAKE(dev_priv, reg) \
         (((dev_priv)->info->gen >= 6) && \
          ((reg) < 0x40000) &&            \
-         ((reg) != FORCEWAKE) &&         \
-         ((reg) != ECOBUS))
+         ((reg) != FORCEWAKE))
 
 #define __i915_read(x, y) \
         u##x i915_read##x(struct drm_i915_private *dev_priv, u32 reg);
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index cb21d5bbeccb..ff99fa267bf6 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -8591,9 +8591,15 @@ static void intel_init_display(struct drm_device *dev)
                 if (IS_IVYBRIDGE(dev)) {
                         u32     ecobus;
 
+                        /* A small trick here - if the bios hasn't configured MT forcewake,
+                         * and if the device is in RC6, then force_wake_mt_get will not wake
+                         * the device and the ECOBUS read will return zero. Which will be
+                         * (correctly) interpreted by the test below as MT forcewake being
+                         * disabled.
+                         */
                         mutex_lock(&dev->struct_mutex);
                         __gen6_gt_force_wake_mt_get(dev_priv);
-                        ecobus = I915_READ(ECOBUS);
+                        ecobus = I915_READ_NOTRACE(ECOBUS);
                         __gen6_gt_force_wake_mt_put(dev_priv);
                         mutex_unlock(&dev->struct_mutex);